Update/php mailer (#2980)

* Update PHPMailer to  6.1.5

This PR update the bundled version of PHPMAiler

3 files changed, 916 insertions, 553 deletions

diff --git a/lib/PHPMailer/PHPMailer/Exception.php b/lib/PHPMailer/PHPMailer/Exception.php
index 9a05dec3c..b1e552f50 100644
--- a/lib/PHPMailer/PHPMailer/Exception.php
+++ b/lib/PHPMailer/PHPMailer/Exception.php
@@ -23,7 +23,7 @@ namespace PHPMailer\PHPMailer;
 /**
  * PHPMailer exception handler.
  *
- * @author  Marcus Bointon <phpmailer@synchromedia.co.uk>
+ * @author Marcus Bointon <phpmailer@synchromedia.co.uk>
  */
 class Exception extends \Exception
 {
diff --git a/lib/PHPMailer/PHPMailer/PHPMailer.php b/lib/PHPMailer/PHPMailer/PHPMailer.php
index 52104924d..fddad40ac 100644
--- a/lib/PHPMailer/PHPMailer/PHPMailer.php
+++ b/lib/PHPMailer/PHPMailer/PHPMailer.php
@@ -3,13 +3,13 @@
  * PHPMailer - PHP email creation and transport class.
  * PHP Version 5.5.
  *
- * @see       https://github.com/PHPMailer/PHPMailer/ The PHPMailer GitHub project
+ * @see https://github.com/PHPMailer/PHPMailer/ The PHPMailer GitHub project
  *
  * @author    Marcus Bointon (Synchro/coolbru) <phpmailer@synchromedia.co.uk>
  * @author    Jim Jagielski (jimjag) <jimjag@gmail.com>
  * @author    Andy Prevost (codeworxtech) <codeworxtech@users.sourceforge.net>
  * @author    Brent R. Matzelle (original founder)
- * @copyright 2012 - 2017 Marcus Bointon
+ * @copyright 2012 - 2019 Marcus Bointon
  * @copyright 2010 - 2012 Jim Jagielski
  * @copyright 2004 - 2009 Andy Prevost
  * @license   http://www.gnu.org/copyleft/lesser.html GNU Lesser General Public License
@@ -23,13 +23,14 @@ namespace PHPMailer\PHPMailer;
 /**
  * PHPMailer - PHP email creation and transport class.
  *
- * @author  Marcus Bointon (Synchro/coolbru) <phpmailer@synchromedia.co.uk>
- * @author  Jim Jagielski (jimjag) <jimjag@gmail.com>
- * @author  Andy Prevost (codeworxtech) <codeworxtech@users.sourceforge.net>
- * @author  Brent R. Matzelle (original founder)
+ * @author Marcus Bointon (Synchro/coolbru) <phpmailer@synchromedia.co.uk>
+ * @author Jim Jagielski (jimjag) <jimjag@gmail.com>
+ * @author Andy Prevost (codeworxtech) <codeworxtech@users.sourceforge.net>
+ * @author Brent R. Matzelle (original founder)
  */
 class PHPMailer
 {
+    const CHARSET_ASCII = 'us-ascii';
     const CHARSET_ISO88591 = 'iso-8859-1';
     const CHARSET_UTF8 = 'utf-8';
 
@@ -46,12 +47,24 @@ class PHPMailer
     const ENCODING_BINARY = 'binary';
     const ENCODING_QUOTED_PRINTABLE = 'quoted-printable';
 
+    const ENCRYPTION_STARTTLS = 'tls';
+    const ENCRYPTION_SMTPS = 'ssl';
+
+    const ICAL_METHOD_REQUEST = 'REQUEST';
+    const ICAL_METHOD_PUBLISH = 'PUBLISH';
+    const ICAL_METHOD_REPLY = 'REPLY';
+    const ICAL_METHOD_ADD = 'ADD';
+    const ICAL_METHOD_CANCEL = 'CANCEL';
+    const ICAL_METHOD_REFRESH = 'REFRESH';
+    const ICAL_METHOD_COUNTER = 'COUNTER';
+    const ICAL_METHOD_DECLINECOUNTER = 'DECLINECOUNTER';
+
     /**
      * Email priority.
      * Options: null (default), 1 = High, 3 = Normal, 5 = low.
      * When null, the header is not set at all.
      *
-     * @var int
+     * @var int|null
      */
     public $Priority;
 
@@ -146,6 +159,22 @@ class PHPMailer
     public $Ical = '';
 
     /**
+     * Value-array of "method" in Contenttype header "text/calendar"
+     *
+     * @var string[]
+     */
+    protected static $IcalMethods = [
+        self::ICAL_METHOD_REQUEST,
+        self::ICAL_METHOD_PUBLISH,
+        self::ICAL_METHOD_REPLY,
+        self::ICAL_METHOD_ADD,
+        self::ICAL_METHOD_CANCEL,
+        self::ICAL_METHOD_REFRESH,
+        self::ICAL_METHOD_COUNTER,
+        self::ICAL_METHOD_DECLINECOUNTER,
+    ];
+
+    /**
      * The complete compiled MIME message body.
      *
      * @var string
@@ -212,6 +241,8 @@ class PHPMailer
      * $_SERVER['SERVER_NAME'], gethostname(), php_uname('n'), or the value
      * 'localhost.localdomain'.
      *
+     * @see PHPMailer::$Helo
+     *
      * @var string
      */
     public $Hostname = '';
@@ -258,7 +289,7 @@ class PHPMailer
     public $Port = 25;
 
     /**
-     * The SMTP HELO of the message.
+     * The SMTP HELO/EHLO name used for the SMTP connection.
      * Default is $Hostname. If $Hostname is empty, PHPMailer attempts to find
      * one with the same method described above for $Hostname.
      *
@@ -270,7 +301,7 @@ class PHPMailer
 
     /**
      * What kind of encryption to use on the SMTP connection.
-     * Options: '', 'ssl' or 'tls'.
+     * Options: '', static::ENCRYPTION_STARTTLS, or static::ENCRYPTION_SMTPS.
      *
      * @var string
      */
@@ -341,14 +372,27 @@ class PHPMailer
     public $Timeout = 300;
 
     /**
+     * Comma separated list of DSN notifications
+     * 'NEVER' under no circumstances a DSN must be returned to the sender.
+     *         If you use NEVER all other notifications will be ignored.
+     * 'SUCCESS' will notify you when your mail has arrived at its destination.
+     * 'FAILURE' will arrive if an error occurred during delivery.
+     * 'DELAY'   will notify you if there is an unusual delay in delivery, but the actual
+     *           delivery's outcome (success or failure) is not yet decided.
+     *
+     * @see https://tools.ietf.org/html/rfc3461 See section 4.1 for more information about NOTIFY
+     */
+    public $dsn = '';
+
+    /**
      * SMTP class debug output mode.
      * Debug output level.
      * Options:
-     * * `0` No output
-     * * `1` Commands
-     * * `2` Data and commands
-     * * `3` As 2 plus connection status
-     * * `4` Low-level data output.
+     * * SMTP::DEBUG_OFF: No output
+     * * SMTP::DEBUG_CLIENT: Client messages
+     * * SMTP::DEBUG_SERVER: Client and server messages
+     * * SMTP::DEBUG_CONNECTION: As SERVER plus connection status
+     * * SMTP::DEBUG_LOWLEVEL: Noisy, low-level data output, rarely needed
      *
      * @see SMTP::$do_debug
      *
@@ -514,9 +558,9 @@ class PHPMailer
 
     /**
      * What to put in the X-Mailer header.
-     * Options: An empty string for PHPMailer default, whitespace for none, or a string to use.
+     * Options: An empty string for PHPMailer default, whitespace/null for none, or a string to use.
      *
-     * @var string
+     * @var string|null
      */
     public $XMailer = '';
 
@@ -701,7 +745,7 @@ class PHPMailer
      *
      * @var string
      */
-    const VERSION = '6.0.7';
+    const VERSION = '6.1.5';
 
     /**
      * Error severity: message only, continue processing.
@@ -725,11 +769,32 @@ class PHPMailer
     const STOP_CRITICAL = 2;
 
     /**
-     * SMTP RFC standard line ending.
+     * The SMTP standard CRLF line break.
+     * If you want to change line break format, change static::$LE, not this.
+     */
+    const CRLF = "\r\n";
+
+    /**
+     * "Folding White Space" a white space string used for line folding.
+     */
+    const FWS = ' ';
+
+    /**
+     * SMTP RFC standard line ending; Carriage Return, Line Feed.
      *
      * @var string
      */
-    protected static $LE = "\r\n";
+    protected static $LE = self::CRLF;
+
+    /**
+     * The maximum line length supported by mail().
+     *
+     * Background: mail() will sometimes corrupt messages
+     * with headers headers longer than 65 chars, see #818.
+     *
+     * @var int
+     */
+    const MAIL_MAX_LINE_LENGTH = 63;
 
     /**
      * The maximum line length allowed by RFC 2822 section 2.1.1.
@@ -794,7 +859,7 @@ class PHPMailer
             $subject = $this->encodeHeader($this->secureHeader($subject));
         }
         //Calling mail() with null params breaks
-        if (!$this->UseSendmailOptions or null === $params) {
+        if (!$this->UseSendmailOptions || null === $params) {
             $result = @mail($to, $subject, $body, $header);
         } else {
             $result = @mail($to, $subject, $body, $header, $params);
@@ -824,7 +889,7 @@ class PHPMailer
             return;
         }
         //Avoid clash with built-in function names
-        if (!in_array($this->Debugoutput, ['error_log', 'html', 'echo']) and is_callable($this->Debugoutput)) {
+        if (is_callable($this->Debugoutput) && !in_array($this->Debugoutput, ['error_log', 'html', 'echo'])) {
             call_user_func($this->Debugoutput, $str, $this->SMTPDebug);
 
             return;
@@ -845,12 +910,12 @@ class PHPMailer
             case 'echo':
             default:
                 //Normalize line breaks
-                $str = preg_replace('/\r\n|\r/ms', "\n", $str);
+                $str = preg_replace('/\r\n|\r/m', "\n", $str);
                 echo gmdate('Y-m-d H:i:s'),
                 "\t",
                     //Trim trailing space
                 trim(
-                //Indent for readability, except for trailing break
+                    //Indent for readability, except for trailing break
                     str_replace(
                         "\n",
                         "\n                   \t                  ",
@@ -927,6 +992,8 @@ class PHPMailer
      * @param string $address The email address to send to
      * @param string $name
      *
+     * @throws Exception
+     *
      * @return bool true on success, false if address already used or invalid in some way
      */
     public function addAddress($address, $name = '')
@@ -940,6 +1007,8 @@ class PHPMailer
      * @param string $address The email address to send to
      * @param string $name
      *
+     * @throws Exception
+     *
      * @return bool true on success, false if address already used or invalid in some way
      */
     public function addCC($address, $name = '')
@@ -953,6 +1022,8 @@ class PHPMailer
      * @param string $address The email address to send to
      * @param string $name
      *
+     * @throws Exception
+     *
      * @return bool true on success, false if address already used or invalid in some way
      */
     public function addBCC($address, $name = '')
@@ -966,6 +1037,8 @@ class PHPMailer
      * @param string $address The email address to reply to
      * @param string $name
      *
+     * @throws Exception
+     *
      * @return bool true on success, false if address already used or invalid in some way
      */
     public function addReplyTo($address, $name = '')
@@ -994,10 +1067,12 @@ class PHPMailer
         $pos = strrpos($address, '@');
         if (false === $pos) {
             // At-sign is missing.
-            $error_message = sprintf('%s (%s): %s',
+            $error_message = sprintf(
+                '%s (%s): %s',
                 $this->lang('invalid_address'),
                 $kind,
-                $address);
+                $address
+            );
             $this->setError($error_message);
             $this->edebug($error_message);
             if ($this->exceptions) {
@@ -1008,19 +1083,17 @@ class PHPMailer
         }
         $params = [$kind, $address, $name];
         // Enqueue addresses with IDN until we know the PHPMailer::$CharSet.
-        if ($this->has8bitChars(substr($address, ++$pos)) and static::idnSupported()) {
-            if ('Reply-To' != $kind) {
+        if (static::idnSupported() && $this->has8bitChars(substr($address, ++$pos))) {
+            if ('Reply-To' !== $kind) {
                 if (!array_key_exists($address, $this->RecipientsQueue)) {
                     $this->RecipientsQueue[$address] = $params;
 
                     return true;
                 }
-            } else {
-                if (!array_key_exists($address, $this->ReplyToQueue)) {
-                    $this->ReplyToQueue[$address] = $params;
+            } elseif (!array_key_exists($address, $this->ReplyToQueue)) {
+                $this->ReplyToQueue[$address] = $params;
 
-                    return true;
-                }
+                return true;
             }
 
             return false;
@@ -1045,9 +1118,11 @@ class PHPMailer
     protected function addAnAddress($kind, $address, $name = '')
     {
         if (!in_array($kind, ['to', 'cc', 'bcc', 'Reply-To'])) {
-            $error_message = sprintf('%s: %s',
+            $error_message = sprintf(
+                '%s: %s',
                 $this->lang('Invalid recipient kind'),
-                $kind);
+                $kind
+            );
             $this->setError($error_message);
             $this->edebug($error_message);
             if ($this->exceptions) {
@@ -1057,10 +1132,12 @@ class PHPMailer
             return false;
         }
         if (!static::validateAddress($address)) {
-            $error_message = sprintf('%s (%s): %s',
+            $error_message = sprintf(
+                '%s (%s): %s',
                 $this->lang('invalid_address'),
                 $kind,
-                $address);
+                $address
+            );
             $this->setError($error_message);
             $this->edebug($error_message);
             if ($this->exceptions) {
@@ -1069,19 +1146,17 @@ class PHPMailer
 
             return false;
         }
-        if ('Reply-To' != $kind) {
+        if ('Reply-To' !== $kind) {
             if (!array_key_exists(strtolower($address), $this->all_recipients)) {
                 $this->{$kind}[] = [$address, $name];
                 $this->all_recipients[strtolower($address)] = true;
 
                 return true;
             }
-        } else {
-            if (!array_key_exists(strtolower($address), $this->ReplyTo)) {
-                $this->ReplyTo[strtolower($address)] = [$address, $name];
+        } elseif (!array_key_exists(strtolower($address), $this->ReplyTo)) {
+            $this->ReplyTo[strtolower($address)] = [$address, $name];
 
-                return true;
-            }
+            return true;
         }
 
         return false;
@@ -1093,7 +1168,7 @@ class PHPMailer
      * Uses the imap_rfc822_parse_adrlist function if the IMAP extension is available.
      * Note that quotes in the name part are removed.
      *
-     * @see    http://www.andrew.cmu.edu/user/agreen1/testing/mrbs/web/Mail/RFC822.php A more careful implementation
+     * @see http://www.andrew.cmu.edu/user/agreen1/testing/mrbs/web/Mail/RFC822.php A more careful implementation
      *
      * @param string $addrstr The address list string
      * @param bool   $useimap Whether to use the IMAP extension to parse the list
@@ -1103,17 +1178,17 @@ class PHPMailer
     public static function parseAddresses($addrstr, $useimap = true)
     {
         $addresses = [];
-        if ($useimap and function_exists('imap_rfc822_parse_adrlist')) {
+        if ($useimap && function_exists('imap_rfc822_parse_adrlist')) {
             //Use this built-in parser if it's available
             $list = imap_rfc822_parse_adrlist($addrstr, '');
             foreach ($list as $address) {
-                if ('.SYNTAX-ERROR.' != $address->host) {
-                    if (static::validateAddress($address->mailbox . '@' . $address->host)) {
-                        $addresses[] = [
-                            'name' => (property_exists($address, 'personal') ? $address->personal : ''),
-                            'address' => $address->mailbox . '@' . $address->host,
-                        ];
-                    }
+                if (('.SYNTAX-ERROR.' !== $address->host) && static::validateAddress(
+                    $address->mailbox . '@' . $address->host
+                )) {
+                    $addresses[] = [
+                        'name' => (property_exists($address, 'personal') ? $address->personal : ''),
+                        'address' => $address->mailbox . '@' . $address->host,
+                    ];
                 }
             }
         } else {
@@ -1163,12 +1238,15 @@ class PHPMailer
         $name = trim(preg_replace('/[\r\n]+/', '', $name)); //Strip breaks and trim
         // Don't validate now addresses with IDN. Will be done in send().
         $pos = strrpos($address, '@');
-        if (false === $pos or
-            (!$this->has8bitChars(substr($address, ++$pos)) or !static::idnSupported()) and
-            !static::validateAddress($address)) {
-            $error_message = sprintf('%s (From): %s',
+        if ((false === $pos)
+            || ((!$this->has8bitChars(substr($address, ++$pos)) || !static::idnSupported())
+            && !static::validateAddress($address))
+        ) {
+            $error_message = sprintf(
+                '%s (From): %s',
                 $this->lang('invalid_address'),
-                $address);
+                $address
+            );
             $this->setError($error_message);
             $this->edebug($error_message);
             if ($this->exceptions) {
@@ -1179,10 +1257,8 @@ class PHPMailer
         }
         $this->From = $address;
         $this->FromName = $name;
-        if ($auto) {
-            if (empty($this->Sender)) {
-                $this->Sender = $address;
-            }
+        if ($auto && empty($this->Sender)) {
+            $this->Sender = $address;
         }
 
         return true;
@@ -1231,10 +1307,10 @@ class PHPMailer
             $patternselect = static::$validator;
         }
         if (is_callable($patternselect)) {
-            return call_user_func($patternselect, $address);
+            return $patternselect($address);
         }
         //Reject line breaks in addresses; it's valid RFC5322, but not RFC5321
-        if (strpos($address, "\n") !== false or strpos($address, "\r") !== false) {
+        if (strpos($address, "\n") !== false || strpos($address, "\r") !== false) {
             return false;
         }
         switch ($patternselect) {
@@ -1281,7 +1357,7 @@ class PHPMailer
                 );
             case 'php':
             default:
-                return (bool) filter_var($address, FILTER_VALIDATE_EMAIL);
+                return filter_var($address, FILTER_VALIDATE_EMAIL) !== false;
         }
     }
 
@@ -1293,7 +1369,7 @@ class PHPMailer
      */
     public static function idnSupported()
     {
-        return function_exists('idn_to_ascii') and function_exists('mb_convert_encoding');
+        return function_exists('idn_to_ascii') && function_exists('mb_convert_encoding');
     }
 
     /**
@@ -1304,7 +1380,7 @@ class PHPMailer
      * - Conversion to punycode is impossible (e.g. required PHP functions are not available)
      *   or fails for any reason (e.g. domain contains characters not allowed in an IDN).
      *
-     * @see    PHPMailer::$CharSet
+     * @see PHPMailer::$CharSet
      *
      * @param string $address The email address to convert
      *
@@ -1314,17 +1390,23 @@ class PHPMailer
     {
         // Verify we have required functions, CharSet, and at-sign.
         $pos = strrpos($address, '@');
-        if (static::idnSupported() and
-            !empty($this->CharSet) and
-            false !== $pos
+        if (!empty($this->CharSet) &&
+            false !== $pos &&
+            static::idnSupported()
         ) {
             $domain = substr($address, ++$pos);
             // Verify CharSet string is a valid one, and domain properly encoded in this CharSet.
-            if ($this->has8bitChars($domain) and @mb_check_encoding($domain, $this->CharSet)) {
+            if ($this->has8bitChars($domain) && @mb_check_encoding($domain, $this->CharSet)) {
                 $domain = mb_convert_encoding($domain, 'UTF-8', $this->CharSet);
                 //Ignore IDE complaints about this line - method signature changed in PHP 5.4
                 $errorcode = 0;
-                $punycode = idn_to_ascii($domain, $errorcode, INTL_IDNA_VARIANT_UTS46);
+                if (defined('INTL_IDNA_VARIANT_UTS46')) {
+                    $punycode = idn_to_ascii($domain, $errorcode, INTL_IDNA_VARIANT_UTS46);
+                } elseif (defined('INTL_IDNA_VARIANT_2003')) {
+                    $punycode = idn_to_ascii($domain, $errorcode, INTL_IDNA_VARIANT_2003);
+                } else {
+                    $punycode = idn_to_ascii($domain, $errorcode);
+                }
                 if (false !== $punycode) {
                     return substr($address, 0, $pos) . $punycode;
                 }
@@ -1370,24 +1452,22 @@ class PHPMailer
      */
     public function preSend()
     {
-        if ('smtp' == $this->Mailer or
-            ('mail' == $this->Mailer and stripos(PHP_OS, 'WIN') === 0)
+        if ('smtp' === $this->Mailer
+            || ('mail' === $this->Mailer && stripos(PHP_OS, 'WIN') === 0)
         ) {
             //SMTP mandates RFC-compliant line endings
             //and it's also used with mail() on Windows
-            static::setLE("\r\n");
+            static::setLE(self::CRLF);
         } else {
             //Maintain backward compatibility with legacy Linux command line mailers
             static::setLE(PHP_EOL);
         }
         //Check for buggy PHP versions that add a header with an incorrect line break
-        if (ini_get('mail.add_x_header') == 1
-            and 'mail' == $this->Mailer
-            and stripos(PHP_OS, 'WIN') === 0
-            and ((version_compare(PHP_VERSION, '7.0.0', '>=')
-                    and version_compare(PHP_VERSION, '7.0.17', '<'))
-                or (version_compare(PHP_VERSION, '7.1.0', '>=')
-                    and version_compare(PHP_VERSION, '7.1.3', '<')))
+        if ('mail' === $this->Mailer
+            && ((PHP_VERSION_ID >= 70000 && PHP_VERSION_ID < 70017)
+                || (PHP_VERSION_ID >= 70100 && PHP_VERSION_ID < 70103))
+            && ini_get('mail.add_x_header') === '1'
+            && stripos(PHP_OS, 'WIN') === 0
         ) {
             trigger_error(
                 'Your version of PHP is affected by a bug that may result in corrupted messages.' .
@@ -1418,10 +1498,12 @@ class PHPMailer
                 }
                 $this->$address_kind = $this->punyencodeAddress($this->$address_kind);
                 if (!static::validateAddress($this->$address_kind)) {
-                    $error_message = sprintf('%s (%s): %s',
+                    $error_message = sprintf(
+                        '%s (%s): %s',
                         $this->lang('invalid_address'),
                         $address_kind,
-                        $this->$address_kind);
+                        $this->$address_kind
+                    );
                     $this->setError($error_message);
                     $this->edebug($error_message);
                     if ($this->exceptions) {
@@ -1439,7 +1521,7 @@ class PHPMailer
 
             $this->setMessageType();
             // Refuse to send an empty message unless we are specifically allowing it
-            if (!$this->AllowEmpty and empty($this->Body)) {
+            if (!$this->AllowEmpty && empty($this->Body)) {
                 throw new Exception($this->lang('empty_message'), self::STOP_CRITICAL);
             }
 
@@ -1455,7 +1537,7 @@ class PHPMailer
 
             // To capture the complete message when using mail(), create
             // an extra header list which createHeader() doesn't fold in
-            if ('mail' == $this->Mailer) {
+            if ('mail' === $this->Mailer) {
                 if (count($this->to) > 0) {
                     $this->mailHeader .= $this->addrAppend('To', $this->to);
                 } else {
@@ -1469,11 +1551,11 @@ class PHPMailer
 
             // Sign with DKIM if enabled
             if (!empty($this->DKIM_domain)
-                and !empty($this->DKIM_selector)
-                and (!empty($this->DKIM_private_string)
-                    or (!empty($this->DKIM_private)
-                        and static::isPermittedPath($this->DKIM_private)
-                        and file_exists($this->DKIM_private)
+                && !empty($this->DKIM_selector)
+                && (!empty($this->DKIM_private_string)
+                    || (!empty($this->DKIM_private)
+                        && static::isPermittedPath($this->DKIM_private)
+                        && file_exists($this->DKIM_private)
                     )
                 )
             ) {
@@ -1482,7 +1564,7 @@ class PHPMailer
                     $this->encodeHeader($this->secureHeader($this->Subject)),
                     $this->MIMEBody
                 );
-                $this->MIMEHeader = rtrim($this->MIMEHeader, "\r\n ") . static::$LE .
+                $this->MIMEHeader = static::stripTrailingWSP($this->MIMEHeader) . static::$LE .
                     static::normalizeBreaks($header_dkim) . static::$LE;
             }
 
@@ -1538,7 +1620,7 @@ class PHPMailer
     /**
      * Send mail using the $Sendmail program.
      *
-     * @see    PHPMailer::$Sendmail
+     * @see PHPMailer::$Sendmail
      *
      * @param string $header The message headers
      * @param string $body   The message body
@@ -1549,19 +1631,19 @@ class PHPMailer
      */
     protected function sendmailSend($header, $body)
     {
+        $header = static::stripTrailingWSP($header) . static::$LE . static::$LE;
+
         // CVE-2016-10033, CVE-2016-10045: Don't pass -f if characters will be escaped.
-        if (!empty($this->Sender) and self::isShellSafe($this->Sender)) {
-            if ('qmail' == $this->Mailer) {
+        if (!empty($this->Sender) && self::isShellSafe($this->Sender)) {
+            if ('qmail' === $this->Mailer) {
                 $sendmailFmt = '%s -f%s';
             } else {
                 $sendmailFmt = '%s -oi -f%s -t';
             }
+        } elseif ('qmail' === $this->Mailer) {
+            $sendmailFmt = '%s';
         } else {
-            if ('qmail' == $this->Mailer) {
-                $sendmailFmt = '%s';
-            } else {
-                $sendmailFmt = '%s -oi -t';
-            }
+            $sendmailFmt = '%s -oi -t';
         }
 
         $sendmail = sprintf($sendmailFmt, escapeshellcmd($this->Sendmail), $this->Sender);
@@ -1577,7 +1659,7 @@ class PHPMailer
                 fwrite($mail, $body);
                 $result = pclose($mail);
                 $this->doCallback(
-                    ($result == 0),
+                    ($result === 0),
                     [$toAddr],
                     $this->cc,
                     $this->bcc,
@@ -1599,7 +1681,7 @@ class PHPMailer
             fwrite($mail, $body);
             $result = pclose($mail);
             $this->doCallback(
-                ($result == 0),
+                ($result === 0),
                 $this->to,
                 $this->cc,
                 $this->bcc,
@@ -1630,7 +1712,7 @@ class PHPMailer
     {
         // Future-proof
         if (escapeshellcmd($string) !== $string
-            or !in_array(escapeshellarg($string), ["'$string'", "\"$string\""])
+            || !in_array(escapeshellarg($string), ["'$string'", "\"$string\""])
         ) {
             return false;
         }
@@ -1668,7 +1750,7 @@ class PHPMailer
     /**
      * Send mail using the PHP mail() function.
      *
-     * @see    http://www.php.net/manual/en/book.mail.php
+     * @see http://www.php.net/manual/en/book.mail.php
      *
      * @param string $header The message headers
      * @param string $body   The message body
@@ -1679,6 +1761,8 @@ class PHPMailer
      */
     protected function mailSend($header, $body)
     {
+        $header = static::stripTrailingWSP($header) . static::$LE . static::$LE;
+
         $toArr = [];
         foreach ($this->to as $toaddr) {
             $toArr[] = $this->addrFormat($toaddr);
@@ -1687,24 +1771,22 @@ class PHPMailer
 
         $params = null;
         //This sets the SMTP envelope sender which gets turned into a return-path header by the receiver
-        if (!empty($this->Sender) and static::validateAddress($this->Sender)) {
-            //A space after `-f` is optional, but there is a long history of its presence
-            //causing problems, so we don't use one
-            //Exim docs: http://www.exim.org/exim-html-current/doc/html/spec_html/ch-the_exim_command_line.html
-            //Sendmail docs: http://www.sendmail.org/~ca/email/man/sendmail.html
-            //Qmail docs: http://www.qmail.org/man/man8/qmail-inject.html
-            //Example problem: https://www.drupal.org/node/1057954
-            // CVE-2016-10033, CVE-2016-10045: Don't pass -f if characters will be escaped.
-            if (self::isShellSafe($this->Sender)) {
-                $params = sprintf('-f%s', $this->Sender);
-            }
+        //A space after `-f` is optional, but there is a long history of its presence
+        //causing problems, so we don't use one
+        //Exim docs: http://www.exim.org/exim-html-current/doc/html/spec_html/ch-the_exim_command_line.html
+        //Sendmail docs: http://www.sendmail.org/~ca/email/man/sendmail.html
+        //Qmail docs: http://www.qmail.org/man/man8/qmail-inject.html
+        //Example problem: https://www.drupal.org/node/1057954
+        // CVE-2016-10033, CVE-2016-10045: Don't pass -f if characters will be escaped.
+        if (!empty($this->Sender) && static::validateAddress($this->Sender) && self::isShellSafe($this->Sender)) {
+            $params = sprintf('-f%s', $this->Sender);
         }
-        if (!empty($this->Sender) and static::validateAddress($this->Sender)) {
+        if (!empty($this->Sender) && static::validateAddress($this->Sender)) {
             $old_from = ini_get('sendmail_from');
             ini_set('sendmail_from', $this->Sender);
         }
         $result = false;
-        if ($this->SingleTo and count($toArr) > 1) {
+        if ($this->SingleTo && count($toArr) > 1) {
             foreach ($toArr as $toAddr) {
                 $result = $this->mailPassthru($toAddr, $this->Subject, $body, $header, $params);
                 $this->doCallback($result, [$toAddr], $this->cc, $this->bcc, $this->Subject, $body, $this->From, []);
@@ -1742,8 +1824,6 @@ class PHPMailer
     /**
      * Provide an instance to use for SMTP operations.
      *
-     * @param SMTP $smtp
-     *
      * @return SMTP
      */
     public function setSMTPInstance(SMTP $smtp)
@@ -1770,12 +1850,13 @@ class PHPMailer
      */
     protected function smtpSend($header, $body)
     {
+        $header = static::stripTrailingWSP($header) . static::$LE . static::$LE;
         $bad_rcpt = [];
         if (!$this->smtpConnect($this->SMTPOptions)) {
             throw new Exception($this->lang('smtp_connect_failed'), self::STOP_CRITICAL);
         }
         //Sender already validated in preSend()
-        if ('' == $this->Sender) {
+        if ('' === $this->Sender) {
             $smtp_from = $this->From;
         } else {
             $smtp_from = $this->Sender;
@@ -1789,7 +1870,7 @@ class PHPMailer
         // Attempt to send to all recipients
         foreach ([$this->to, $this->cc, $this->bcc] as $togroup) {
             foreach ($togroup as $to) {
-                if (!$this->smtp->recipient($to[0])) {
+                if (!$this->smtp->recipient($to[0], $this->dsn)) {
                     $error = $this->smtp->getError();
                     $bad_rcpt[] = ['to' => $to[0], 'error' => $error['detail']];
                     $isSent = false;
@@ -1802,7 +1883,7 @@ class PHPMailer
         }
 
         // Only send the DATA command if we have viable recipients
-        if ((count($this->all_recipients) > count($bad_rcpt)) and !$this->smtp->data($header . $body)) {
+        if ((count($this->all_recipients) > count($bad_rcpt)) && !$this->smtp->data($header . $body)) {
             throw new Exception($this->lang('data_not_accepted'), self::STOP_CRITICAL);
         }
 
@@ -1834,10 +1915,7 @@ class PHPMailer
             foreach ($bad_rcpt as $bad) {
                 $errstr .= $bad['to'] . ': ' . $bad['error'];
             }
-            throw new Exception(
-                $this->lang('recipients_failed') . $errstr,
-                self::STOP_CONTINUE
-            );
+            throw new Exception($this->lang('recipients_failed') . $errstr, self::STOP_CONTINUE);
         }
 
         return true;
@@ -1881,50 +1959,49 @@ class PHPMailer
         foreach ($hosts as $hostentry) {
             $hostinfo = [];
             if (!preg_match(
-                '/^((ssl|tls):\/\/)*([a-zA-Z0-9\.-]*|\[[a-fA-F0-9:]+\]):?([0-9]*)$/',
+                '/^(?:(ssl|tls):\/\/)?(.+?)(?::(\d+))?$/',
                 trim($hostentry),
                 $hostinfo
             )) {
-                static::edebug($this->lang('connect_host') . ' ' . $hostentry);
+                $this->edebug($this->lang('invalid_hostentry') . ' ' . trim($hostentry));
                 // Not a valid host entry
                 continue;
             }
-            // $hostinfo[2]: optional ssl or tls prefix
-            // $hostinfo[3]: the hostname
-            // $hostinfo[4]: optional port number
+            // $hostinfo[1]: optional ssl or tls prefix
+            // $hostinfo[2]: the hostname
+            // $hostinfo[3]: optional port number
             // The host string prefix can temporarily override the current setting for SMTPSecure
             // If it's not specified, the default value is used
 
             //Check the host name is a valid name or IP address before trying to use it
-            if (!static::isValidHost($hostinfo[3])) {
-                static::edebug($this->lang('connect_host') . ' ' . $hostentry);
+            if (!static::isValidHost($hostinfo[2])) {
+                $this->edebug($this->lang('invalid_host') . ' ' . $hostinfo[2]);
                 continue;
             }
             $prefix = '';
             $secure = $this->SMTPSecure;
-            $tls = ('tls' == $this->SMTPSecure);
-            if ('ssl' == $hostinfo[2] or ('' == $hostinfo[2] and 'ssl' == $this->SMTPSecure)) {
+            $tls = (static::ENCRYPTION_STARTTLS === $this->SMTPSecure);
+            if ('ssl' === $hostinfo[1] || ('' === $hostinfo[1] && static::ENCRYPTION_SMTPS === $this->SMTPSecure)) {
                 $prefix = 'ssl://';
                 $tls = false; // Can't have SSL and TLS at the same time
-                $secure = 'ssl';
-            } elseif ('tls' == $hostinfo[2]) {
+                $secure = static::ENCRYPTION_SMTPS;
+            } elseif ('tls' === $hostinfo[1]) {
                 $tls = true;
                 // tls doesn't use a prefix
-                $secure = 'tls';
+                $secure = static::ENCRYPTION_STARTTLS;
             }
             //Do we need the OpenSSL extension?
             $sslext = defined('OPENSSL_ALGO_SHA256');
-            if ('tls' === $secure or 'ssl' === $secure) {
+            if (static::ENCRYPTION_STARTTLS === $secure || static::ENCRYPTION_SMTPS === $secure) {
                 //Check for an OpenSSL constant rather than using extension_loaded, which is sometimes disabled
                 if (!$sslext) {
                     throw new Exception($this->lang('extension_missing') . 'openssl', self::STOP_CRITICAL);
                 }
             }
-            $host = $hostinfo[3];
+            $host = $hostinfo[2];
             $port = $this->Port;
-            $tport = (int) $hostinfo[4];
-            if ($tport > 0 and $tport < 65536) {
-                $port = $tport;
+            if (array_key_exists(3, $hostinfo) && is_numeric($hostinfo[3]) && $hostinfo[3] > 0 && $hostinfo[3] < 65536) {
+                $port = (int) $hostinfo[3];
             }
             if ($this->smtp->connect($prefix . $host, $port, $this->Timeout, $options)) {
                 try {
@@ -1939,7 +2016,7 @@ class PHPMailer
                     // * we have openssl extension
                     // * we are not already using SSL
                     // * the server offers STARTTLS
-                    if ($this->SMTPAutoTLS and $sslext and 'ssl' != $secure and $this->smtp->getServerExt('STARTTLS')) {
+                    if ($this->SMTPAutoTLS && $sslext && 'ssl' !== $secure && $this->smtp->getServerExt('STARTTLS')) {
                         $tls = true;
                     }
                     if ($tls) {
@@ -1949,16 +2026,13 @@ class PHPMailer
                         // We must resend EHLO after TLS negotiation
                         $this->smtp->hello($hello);
                     }
-                    if ($this->SMTPAuth) {
-                        if (!$this->smtp->authenticate(
-                            $this->Username,
-                            $this->Password,
-                            $this->AuthType,
-                            $this->oauth
-                        )
-                        ) {
-                            throw new Exception($this->lang('authenticate'));
-                        }
+                    if ($this->SMTPAuth && !$this->smtp->authenticate(
+                        $this->Username,
+                        $this->Password,
+                        $this->AuthType,
+                        $this->oauth
+                    )) {
+                        throw new Exception($this->lang('authenticate'));
                     }
 
                     return true;
@@ -1973,7 +2047,7 @@ class PHPMailer
         // If we get here, all connection attempts have failed, so close connection hard
         $this->smtp->close();
         // As we've caught all exceptions, just report whatever the last one was
-        if ($this->exceptions and null !== $lastexception) {
+        if ($this->exceptions && null !== $lastexception) {
             throw $lastexception;
         }
 
@@ -1985,11 +2059,9 @@ class PHPMailer
      */
     public function smtpClose()
     {
-        if (null !== $this->smtp) {
-            if ($this->smtp->connected()) {
-                $this->smtp->quit();
-                $this->smtp->close();
-            }
+        if ((null !== $this->smtp) && $this->smtp->connected()) {
+            $this->smtp->quit();
+            $this->smtp->close();
         }
     }
 
@@ -2033,6 +2105,8 @@ class PHPMailer
             'from_failed' => 'The following From address failed: ',
             'instantiate' => 'Could not instantiate mail function.',
             'invalid_address' => 'Invalid address: ',
+            'invalid_hostentry' => 'Invalid hostentry: ',
+            'invalid_host' => 'Invalid host: ',
             'mailer_not_supported' => ' mailer is not supported.',
             'provide_address' => 'You must provide at least one recipient email address.',
             'recipients_failed' => 'SMTP Error: The following recipients failed: ',
@@ -2053,7 +2127,7 @@ class PHPMailer
         $foundlang = true;
         $lang_file = $lang_path . 'phpmailer.lang-' . $langcode . '.php';
         // There is no English translation file
-        if ('en' != $langcode) {
+        if ('en' !== $langcode) {
             // Make sure language file path is readable
             if (!static::isPermittedPath($lang_file) || !file_exists($lang_file)) {
                 $foundlang = false;
@@ -2113,9 +2187,8 @@ class PHPMailer
             return $this->secureHeader($addr[0]);
         }
 
-        return $this->encodeHeader($this->secureHeader($addr[1]), 'phrase') . ' <' . $this->secureHeader(
-                $addr[0]
-            ) . '>';
+        return $this->encodeHeader($this->secureHeader($addr[1]), 'phrase') .
+            ' <' . $this->secureHeader($addr[0]) . '>';
     }
 
     /**
@@ -2145,7 +2218,7 @@ class PHPMailer
 
         $message = static::normalizeBreaks($message);
         //Remove a trailing line break
-        if (substr($message, -$lelen) == static::$LE) {
+        if (substr($message, -$lelen) === static::$LE) {
             $message = substr($message, 0, -$lelen);
         }
 
@@ -2158,16 +2231,16 @@ class PHPMailer
             $buf = '';
             $firstword = true;
             foreach ($words as $word) {
-                if ($qp_mode and (strlen($word) > $length)) {
+                if ($qp_mode && (strlen($word) > $length)) {
                     $space_left = $length - strlen($buf) - $crlflen;
                     if (!$firstword) {
                         if ($space_left > 20) {
                             $len = $space_left;
                             if ($is_utf8) {
                                 $len = $this->utf8CharBoundary($word, $len);
-                            } elseif ('=' == substr($word, $len - 1, 1)) {
+                            } elseif ('=' === substr($word, $len - 1, 1)) {
                                 --$len;
-                            } elseif ('=' == substr($word, $len - 2, 1)) {
+                            } elseif ('=' === substr($word, $len - 2, 1)) {
                                 $len -= 2;
                             }
                             $part = substr($word, 0, $len);
@@ -2179,22 +2252,22 @@ class PHPMailer
                         }
                         $buf = '';
                     }
-                    while (strlen($word) > 0) {
+                    while ($word !== '') {
                         if ($length <= 0) {
                             break;
                         }
                         $len = $length;
                         if ($is_utf8) {
                             $len = $this->utf8CharBoundary($word, $len);
-                        } elseif ('=' == substr($word, $len - 1, 1)) {
+                        } elseif ('=' === substr($word, $len - 1, 1)) {
                             --$len;
-                        } elseif ('=' == substr($word, $len - 2, 1)) {
+                        } elseif ('=' === substr($word, $len - 2, 1)) {
                             $len -= 2;
                         }
                         $part = substr($word, 0, $len);
-                        $word = substr($word, $len);
+                        $word = (string) substr($word, $len);
 
-                        if (strlen($word) > 0) {
+                        if ($word !== '') {
                             $message .= $part . sprintf('=%s', static::$LE);
                         } else {
                             $buf = $part;
@@ -2207,7 +2280,7 @@ class PHPMailer
                     }
                     $buf .= $word;
 
-                    if (strlen($buf) > $length and '' != $buf_o) {
+                    if ('' !== $buf_o && strlen($buf) > $length) {
                         $message .= $buf_o . $soft_break;
                         $buf = $word;
                     }
@@ -2302,23 +2375,21 @@ class PHPMailer
     {
         $result = '';
 
-        $result .= $this->headerLine('Date', '' == $this->MessageDate ? self::rfcDate() : $this->MessageDate);
+        $result .= $this->headerLine('Date', '' === $this->MessageDate ? self::rfcDate() : $this->MessageDate);
 
         // To be created automatically by mail()
         if ($this->SingleTo) {
-            if ('mail' != $this->Mailer) {
+            if ('mail' !== $this->Mailer) {
                 foreach ($this->to as $toaddr) {
                     $this->SingleToArray[] = $this->addrFormat($toaddr);
                 }
             }
-        } else {
-            if (count($this->to) > 0) {
-                if ('mail' != $this->Mailer) {
-                    $result .= $this->addrAppend('To', $this->to);
-                }
-            } elseif (count($this->cc) == 0) {
-                $result .= $this->headerLine('To', 'undisclosed-recipients:;');
+        } elseif (count($this->to) > 0) {
+            if ('mail' !== $this->Mailer) {
+                $result .= $this->addrAppend('To', $this->to);
             }
+        } elseif (count($this->cc) === 0) {
+            $result .= $this->headerLine('To', 'undisclosed-recipients:;');
         }
 
         $result .= $this->addrAppend('From', [[trim($this->From), $this->FromName]]);
@@ -2330,9 +2401,9 @@ class PHPMailer
 
         // sendmail and mail() extract Bcc from the header before sending
         if ((
-                'sendmail' == $this->Mailer or 'qmail' == $this->Mailer or 'mail' == $this->Mailer
+                'sendmail' === $this->Mailer || 'qmail' === $this->Mailer || 'mail' === $this->Mailer
             )
-            and count($this->bcc) > 0
+            && count($this->bcc) > 0
         ) {
             $result .= $this->addrAppend('Bcc', $this->bcc);
         }
@@ -2342,13 +2413,13 @@ class PHPMailer
         }
 
         // mail() sets the subject itself
-        if ('mail' != $this->Mailer) {
+        if ('mail' !== $this->Mailer) {
             $result .= $this->headerLine('Subject', $this->encodeHeader($this->secureHeader($this->Subject)));
         }
 
         // Only allow a custom message ID if it conforms to RFC 5322 section 3.6.4
         // https://tools.ietf.org/html/rfc5322#section-3.6.4
-        if ('' != $this->MessageID and preg_match('/^<.*@.*>$/', $this->MessageID)) {
+        if ('' !== $this->MessageID && preg_match('/^<.*@.*>$/', $this->MessageID)) {
             $this->lastMessageID = $this->MessageID;
         } else {
             $this->lastMessageID = sprintf('<%s@%s>', $this->uniqueid, $this->serverHostname());
@@ -2357,7 +2428,7 @@ class PHPMailer
         if (null !== $this->Priority) {
             $result .= $this->headerLine('X-Priority', $this->Priority);
         }
-        if ('' == $this->XMailer) {
+        if ('' === $this->XMailer) {
             $result .= $this->headerLine(
                 'X-Mailer',
                 'PHPMailer ' . self::VERSION . ' (https://github.com/PHPMailer/PHPMailer)'
@@ -2369,7 +2440,7 @@ class PHPMailer
             }
         }
 
-        if ('' != $this->ConfirmReadingTo) {
+        if ('' !== $this->ConfirmReadingTo) {
             $result .= $this->headerLine('Disposition-Notification-To', '<' . $this->ConfirmReadingTo . '>');
         }
 
@@ -2400,19 +2471,19 @@ class PHPMailer
         switch ($this->message_type) {
             case 'inline':
                 $result .= $this->headerLine('Content-Type', static::CONTENT_TYPE_MULTIPART_RELATED . ';');
-                $result .= $this->textLine("\tboundary=\"" . $this->boundary[1] . '"');
+                $result .= $this->textLine(' boundary="' . $this->boundary[1] . '"');
                 break;
             case 'attach':
             case 'inline_attach':
             case 'alt_attach':
             case 'alt_inline_attach':
                 $result .= $this->headerLine('Content-Type', static::CONTENT_TYPE_MULTIPART_MIXED . ';');
-                $result .= $this->textLine("\tboundary=\"" . $this->boundary[1] . '"');
+                $result .= $this->textLine(' boundary="' . $this->boundary[1] . '"');
                 break;
             case 'alt':
             case 'alt_inline':
                 $result .= $this->headerLine('Content-Type', static::CONTENT_TYPE_MULTIPART_ALTERNATIVE . ';');
-                $result .= $this->textLine("\tboundary=\"" . $this->boundary[1] . '"');
+                $result .= $this->textLine(' boundary="' . $this->boundary[1] . '"');
                 break;
             default:
                 // Catches case 'plain': and case '':
@@ -2421,10 +2492,10 @@ class PHPMailer
                 break;
         }
         // RFC1341 part 5 says 7bit is assumed if not specified
-        if (static::ENCODING_7BIT != $this->Encoding) {
+        if (static::ENCODING_7BIT !== $this->Encoding) {
             // RFC 2045 section 6.4 says multipart MIME parts may only use 7bit, 8bit or binary CTE
             if ($ismultipart) {
-                if (static::ENCODING_8BIT == $this->Encoding) {
+                if (static::ENCODING_8BIT === $this->Encoding) {
                     $result .= $this->headerLine('Content-Transfer-Encoding', static::ENCODING_8BIT);
                 }
                 // The only remaining alternatives are quoted-printable and base64, which are both 7bit compatible
@@ -2433,8 +2504,8 @@ class PHPMailer
             }
         }
 
-        if ('mail' != $this->Mailer) {
-            $result .= static::$LE;
+        if ('mail' !== $this->Mailer) {
+//            $result .= static::$LE;
         }
 
         return $result;
@@ -2451,7 +2522,8 @@ class PHPMailer
      */
     public function getSentMIMEMessage()
     {
-        return rtrim($this->MIMEHeader . $this->mailHeader, "\n\r") . static::$LE . static::$LE . $this->MIMEBody;
+        return static::stripTrailingWSP($this->MIMEHeader . $this->mailHeader) .
+            static::$LE . static::$LE . $this->MIMEBody;
     }
 
     /**
@@ -2462,11 +2534,19 @@ class PHPMailer
     protected function generateId()
     {
         $len = 32; //32 bytes = 256 bits
+        $bytes = '';
         if (function_exists('random_bytes')) {
-            $bytes = random_bytes($len);
+            try {
+                $bytes = random_bytes($len);
+            } catch (\Exception $e) {
+                //Do nothing
+            }
         } elseif (function_exists('openssl_random_pseudo_bytes')) {
+            /** @noinspection CryptographicallySecureRandomnessInspection */
             $bytes = openssl_random_pseudo_bytes($len);
-        } else {
+        }
+        if ($bytes === '') {
+            //We failed to produce a proper random string, so make do.
             //Use a hash to force the length to the same as the other methods
             $bytes = hash('sha256', uniqid((string) mt_rand(), true), true);
         }
@@ -2501,32 +2581,32 @@ class PHPMailer
         $bodyEncoding = $this->Encoding;
         $bodyCharSet = $this->CharSet;
         //Can we do a 7-bit downgrade?
-        if (static::ENCODING_8BIT == $bodyEncoding and !$this->has8bitChars($this->Body)) {
+        if (static::ENCODING_8BIT === $bodyEncoding && !$this->has8bitChars($this->Body)) {
             $bodyEncoding = static::ENCODING_7BIT;
             //All ISO 8859, Windows codepage and UTF-8 charsets are ascii compatible up to 7-bit
-            $bodyCharSet = 'us-ascii';
+            $bodyCharSet = static::CHARSET_ASCII;
         }
         //If lines are too long, and we're not already using an encoding that will shorten them,
         //change to quoted-printable transfer encoding for the body part only
-        if (static::ENCODING_BASE64 != $this->Encoding and static::hasLineLongerThanMax($this->Body)) {
+        if (static::ENCODING_BASE64 !== $this->Encoding && static::hasLineLongerThanMax($this->Body)) {
             $bodyEncoding = static::ENCODING_QUOTED_PRINTABLE;
         }
 
         $altBodyEncoding = $this->Encoding;
         $altBodyCharSet = $this->CharSet;
         //Can we do a 7-bit downgrade?
-        if (static::ENCODING_8BIT == $altBodyEncoding and !$this->has8bitChars($this->AltBody)) {
+        if (static::ENCODING_8BIT === $altBodyEncoding && !$this->has8bitChars($this->AltBody)) {
             $altBodyEncoding = static::ENCODING_7BIT;
             //All ISO 8859, Windows codepage and UTF-8 charsets are ascii compatible up to 7-bit
-            $altBodyCharSet = 'us-ascii';
+            $altBodyCharSet = static::CHARSET_ASCII;
         }
         //If lines are too long, and we're not already using an encoding that will shorten them,
         //change to quoted-printable transfer encoding for the alt body part only
-        if (static::ENCODING_BASE64 != $altBodyEncoding and static::hasLineLongerThanMax($this->AltBody)) {
+        if (static::ENCODING_BASE64 !== $altBodyEncoding && static::hasLineLongerThanMax($this->AltBody)) {
             $altBodyEncoding = static::ENCODING_QUOTED_PRINTABLE;
         }
         //Use this as a preamble in all multipart message types
-        $mimepre = 'This is a multi-part message in MIME format.' . static::$LE;
+        $mimepre = 'This is a multi-part message in MIME format.' . static::$LE  . static::$LE;
         switch ($this->message_type) {
             case 'inline':
                 $body .= $mimepre;
@@ -2546,7 +2626,8 @@ class PHPMailer
                 $body .= $mimepre;
                 $body .= $this->textLine('--' . $this->boundary[1]);
                 $body .= $this->headerLine('Content-Type', static::CONTENT_TYPE_MULTIPART_RELATED . ';');
-                $body .= $this->textLine("\tboundary=\"" . $this->boundary[2] . '"');
+                $body .= $this->textLine(' boundary="' . $this->boundary[2] . '";');
+                $body .= $this->textLine(' type="' . static::CONTENT_TYPE_TEXT_HTML . '"');
                 $body .= static::$LE;
                 $body .= $this->getBoundary($this->boundary[2], $bodyCharSet, '', $bodyEncoding);
                 $body .= $this->encodeString($this->Body, $bodyEncoding);
@@ -2557,14 +2638,36 @@ class PHPMailer
                 break;
             case 'alt':
                 $body .= $mimepre;
-                $body .= $this->getBoundary($this->boundary[1], $altBodyCharSet, static::CONTENT_TYPE_PLAINTEXT, $altBodyEncoding);
+                $body .= $this->getBoundary(
+                    $this->boundary[1],
+                    $altBodyCharSet,
+                    static::CONTENT_TYPE_PLAINTEXT,
+                    $altBodyEncoding
+                );
                 $body .= $this->encodeString($this->AltBody, $altBodyEncoding);
                 $body .= static::$LE;
-                $body .= $this->getBoundary($this->boundary[1], $bodyCharSet, static::CONTENT_TYPE_TEXT_HTML, $bodyEncoding);
+                $body .= $this->getBoundary(
+                    $this->boundary[1],
+                    $bodyCharSet,
+                    static::CONTENT_TYPE_TEXT_HTML,
+                    $bodyEncoding
+                );
                 $body .= $this->encodeString($this->Body, $bodyEncoding);
                 $body .= static::$LE;
                 if (!empty($this->Ical)) {
-                    $body .= $this->getBoundary($this->boundary[1], '', static::CONTENT_TYPE_TEXT_CALENDAR . '; method=REQUEST', '');
+                    $method = static::ICAL_METHOD_REQUEST;
+                    foreach (static::$IcalMethods as $imethod) {
+                        if (stripos($this->Ical, 'METHOD:' . $imethod) !== false) {
+                            $method = $imethod;
+                            break;
+                        }
+                    }
+                    $body .= $this->getBoundary(
+                        $this->boundary[1],
+                        '',
+                        static::CONTENT_TYPE_TEXT_CALENDAR . '; method=' . $method,
+                        ''
+                    );
                     $body .= $this->encodeString($this->Ical, $this->Encoding);
                     $body .= static::$LE;
                 }
@@ -2572,14 +2675,25 @@ class PHPMailer
                 break;
             case 'alt_inline':
                 $body .= $mimepre;
-                $body .= $this->getBoundary($this->boundary[1], $altBodyCharSet, static::CONTENT_TYPE_PLAINTEXT, $altBodyEncoding);
+                $body .= $this->getBoundary(
+                    $this->boundary[1],
+                    $altBodyCharSet,
+                    static::CONTENT_TYPE_PLAINTEXT,
+                    $altBodyEncoding
+                );
                 $body .= $this->encodeString($this->AltBody, $altBodyEncoding);
                 $body .= static::$LE;
                 $body .= $this->textLine('--' . $this->boundary[1]);
                 $body .= $this->headerLine('Content-Type', static::CONTENT_TYPE_MULTIPART_RELATED . ';');
-                $body .= $this->textLine("\tboundary=\"" . $this->boundary[2] . '"');
+                $body .= $this->textLine(' boundary="' . $this->boundary[2] . '";');
+                $body .= $this->textLine(' type="' . static::CONTENT_TYPE_TEXT_HTML . '"');
                 $body .= static::$LE;
-                $body .= $this->getBoundary($this->boundary[2], $bodyCharSet, static::CONTENT_TYPE_TEXT_HTML, $bodyEncoding);
+                $body .= $this->getBoundary(
+                    $this->boundary[2],
+                    $bodyCharSet,
+                    static::CONTENT_TYPE_TEXT_HTML,
+                    $bodyEncoding
+                );
                 $body .= $this->encodeString($this->Body, $bodyEncoding);
                 $body .= static::$LE;
                 $body .= $this->attachAll('inline', $this->boundary[2]);
@@ -2590,16 +2704,38 @@ class PHPMailer
                 $body .= $mimepre;
                 $body .= $this->textLine('--' . $this->boundary[1]);
                 $body .= $this->headerLine('Content-Type', static::CONTENT_TYPE_MULTIPART_ALTERNATIVE . ';');
-                $body .= $this->textLine("\tboundary=\"" . $this->boundary[2] . '"');
+                $body .= $this->textLine(' boundary="' . $this->boundary[2] . '"');
                 $body .= static::$LE;
-                $body .= $this->getBoundary($this->boundary[2], $altBodyCharSet, static::CONTENT_TYPE_PLAINTEXT, $altBodyEncoding);
+                $body .= $this->getBoundary(
+                    $this->boundary[2],
+                    $altBodyCharSet,
+                    static::CONTENT_TYPE_PLAINTEXT,
+                    $altBodyEncoding
+                );
                 $body .= $this->encodeString($this->AltBody, $altBodyEncoding);
                 $body .= static::$LE;
-                $body .= $this->getBoundary($this->boundary[2], $bodyCharSet, static::CONTENT_TYPE_TEXT_HTML, $bodyEncoding);
+                $body .= $this->getBoundary(
+                    $this->boundary[2],
+                    $bodyCharSet,
+                    static::CONTENT_TYPE_TEXT_HTML,
+                    $bodyEncoding
+                );
                 $body .= $this->encodeString($this->Body, $bodyEncoding);
                 $body .= static::$LE;
                 if (!empty($this->Ical)) {
-                    $body .= $this->getBoundary($this->boundary[2], '', static::CONTENT_TYPE_TEXT_CALENDAR . '; method=REQUEST', '');
+                    $method = static::ICAL_METHOD_REQUEST;
+                    foreach (static::$IcalMethods as $imethod) {
+                        if (stripos($this->Ical, 'METHOD:' . $imethod) !== false) {
+                            $method = $imethod;
+                            break;
+                        }
+                    }
+                    $body .= $this->getBoundary(
+                        $this->boundary[2],
+                        '',
+                        static::CONTENT_TYPE_TEXT_CALENDAR . '; method=' . $method,
+                        ''
+                    );
                     $body .= $this->encodeString($this->Ical, $this->Encoding);
                 }
                 $body .= $this->endBoundary($this->boundary[2]);
@@ -2610,16 +2746,27 @@ class PHPMailer
                 $body .= $mimepre;
                 $body .= $this->textLine('--' . $this->boundary[1]);
                 $body .= $this->headerLine('Content-Type', static::CONTENT_TYPE_MULTIPART_ALTERNATIVE . ';');
-                $body .= $this->textLine("\tboundary=\"" . $this->boundary[2] . '"');
+                $body .= $this->textLine(' boundary="' . $this->boundary[2] . '"');
                 $body .= static::$LE;
-                $body .= $this->getBoundary($this->boundary[2], $altBodyCharSet, static::CONTENT_TYPE_PLAINTEXT, $altBodyEncoding);
+                $body .= $this->getBoundary(
+                    $this->boundary[2],
+                    $altBodyCharSet,
+                    static::CONTENT_TYPE_PLAINTEXT,
+                    $altBodyEncoding
+                );
                 $body .= $this->encodeString($this->AltBody, $altBodyEncoding);
                 $body .= static::$LE;
                 $body .= $this->textLine('--' . $this->boundary[2]);
                 $body .= $this->headerLine('Content-Type', static::CONTENT_TYPE_MULTIPART_RELATED . ';');
-                $body .= $this->textLine("\tboundary=\"" . $this->boundary[3] . '"');
+                $body .= $this->textLine(' boundary="' . $this->boundary[3] . '";');
+                $body .= $this->textLine(' type="' . static::CONTENT_TYPE_TEXT_HTML . '"');
                 $body .= static::$LE;
-                $body .= $this->getBoundary($this->boundary[3], $bodyCharSet, static::CONTENT_TYPE_TEXT_HTML, $bodyEncoding);
+                $body .= $this->getBoundary(
+                    $this->boundary[3],
+                    $bodyCharSet,
+                    static::CONTENT_TYPE_TEXT_HTML,
+                    $bodyEncoding
+                );
                 $body .= $this->encodeString($this->Body, $bodyEncoding);
                 $body .= static::$LE;
                 $body .= $this->attachAll('inline', $this->boundary[3]);
@@ -2646,12 +2793,11 @@ class PHPMailer
                 if (!defined('PKCS7_TEXT')) {
                     throw new Exception($this->lang('extension_missing') . 'openssl');
                 }
-                // @TODO would be nice to use php://temp streams here
-                $file = tempnam(sys_get_temp_dir(), 'mail');
-                if (false === file_put_contents($file, $body)) {
-                    throw new Exception($this->lang('signing') . ' Could not write temp file');
-                }
-                $signed = tempnam(sys_get_temp_dir(), 'signed');
+
+                $file = tempnam(sys_get_temp_dir(), 'srcsign');
+                $signed = tempnam(sys_get_temp_dir(), 'mailsign');
+                file_put_contents($file, $body);
+
                 //Workaround for PHP bug https://bugs.php.net/bug.php?id=69197
                 if (empty($this->sign_extracerts_file)) {
                     $sign = @openssl_pkcs7_sign(
@@ -2672,6 +2818,7 @@ class PHPMailer
                         $this->sign_extracerts_file
                     );
                 }
+
                 @unlink($file);
                 if ($sign) {
                     $body = file_get_contents($signed);
@@ -2708,20 +2855,20 @@ class PHPMailer
     protected function getBoundary($boundary, $charSet, $contentType, $encoding)
     {
         $result = '';
-        if ('' == $charSet) {
+        if ('' === $charSet) {
             $charSet = $this->CharSet;
         }
-        if ('' == $contentType) {
+        if ('' === $contentType) {
             $contentType = $this->ContentType;
         }
-        if ('' == $encoding) {
+        if ('' === $encoding) {
             $encoding = $this->Encoding;
         }
         $result .= $this->textLine('--' . $boundary);
         $result .= sprintf('Content-Type: %s; charset=%s', $contentType, $charSet);
         $result .= static::$LE;
         // RFC1341 part 5 says 7bit is assumed if not specified
-        if (static::ENCODING_7BIT != $encoding) {
+        if (static::ENCODING_7BIT !== $encoding) {
             $result .= $this->headerLine('Content-Transfer-Encoding', $encoding);
         }
         $result .= static::$LE;
@@ -2758,7 +2905,7 @@ class PHPMailer
             $type[] = 'attach';
         }
         $this->message_type = implode('_', $type);
-        if ('' == $this->message_type) {
+        if ('' === $this->message_type) {
             //The 'plain' message_type refers to the message having a single body element, not that it is plain-text
             $this->message_type = 'plain';
         }
@@ -2806,23 +2953,32 @@ class PHPMailer
      *
      * @return bool
      */
-    public function addAttachment($path, $name = '', $encoding = self::ENCODING_BASE64, $type = '', $disposition = 'attachment')
-    {
+    public function addAttachment(
+        $path,
+        $name = '',
+        $encoding = self::ENCODING_BASE64,
+        $type = '',
+        $disposition = 'attachment'
+    ) {
         try {
-            if (!static::isPermittedPath($path) || !@is_file($path)) {
+            if (!static::isPermittedPath($path) || !@is_file($path) || !is_readable($path)) {
                 throw new Exception($this->lang('file_access') . $path, self::STOP_CONTINUE);
             }
 
             // If a MIME type is not specified, try to work it out from the file name
-            if ('' == $type) {
+            if ('' === $type) {
                 $type = static::filenameToType($path);
             }
 
-            $filename = basename($path);
-            if ('' == $name) {
+            $filename = (string) static::mb_pathinfo($path, PATHINFO_BASENAME);
+            if ('' === $name) {
                 $name = $filename;
             }
 
+            if (!$this->validateEncoding($encoding)) {
+                throw new Exception($this->lang('encoding') . $encoding);
+            }
+
             $this->attachment[] = [
                 0 => $path,
                 1 => $filename,
@@ -2863,6 +3019,8 @@ class PHPMailer
      * @param string $disposition_type
      * @param string $boundary
      *
+     * @throws Exception
+     *
      * @return string
      */
     protected function attachAll($disposition_type, $boundary)
@@ -2875,7 +3033,7 @@ class PHPMailer
         // Add all attachments
         foreach ($this->attachment as $attachment) {
             // Check if it is a valid disposition_filter
-            if ($attachment[6] == $disposition_type) {
+            if ($attachment[6] === $disposition_type) {
                 // Check for string attachment
                 $string = '';
                 $path = '';
@@ -2887,7 +3045,7 @@ class PHPMailer
                 }
 
                 $inclhash = hash('sha256', serialize($attachment));
-                if (in_array($inclhash, $incl)) {
+                if (in_array($inclhash, $incl, true)) {
                     continue;
                 }
                 $incl[] = $inclhash;
@@ -2896,7 +3054,7 @@ class PHPMailer
                 $type = $attachment[4];
                 $disposition = $attachment[6];
                 $cid = $attachment[7];
-                if ('inline' == $disposition and array_key_exists($cid, $cidUniq)) {
+                if ('inline' === $disposition && array_key_exists($cid, $cidUniq)) {
                     continue;
                 }
                 $cidUniq[$cid] = true;
@@ -2918,42 +3076,41 @@ class PHPMailer
                     );
                 }
                 // RFC1341 part 5 says 7bit is assumed if not specified
-                if (static::ENCODING_7BIT != $encoding) {
+                if (static::ENCODING_7BIT !== $encoding) {
                     $mime[] = sprintf('Content-Transfer-Encoding: %s%s', $encoding, static::$LE);
                 }
 
-                if (!empty($cid)) {
-                    $mime[] = sprintf('Content-ID: <%s>%s', $cid, static::$LE);
+                //Only set Content-IDs on inline attachments
+                if ((string) $cid !== '' && $disposition === 'inline') {
+                    $mime[] = 'Content-ID: <' . $this->encodeHeader($this->secureHeader($cid)) . '>' . static::$LE;
                 }
 
                 // If a filename contains any of these chars, it should be quoted,
                 // but not otherwise: RFC2183 & RFC2045 5.1
                 // Fixes a warning in IETF's msglint MIME checker
                 // Allow for bypassing the Content-Disposition header totally
-                if (!(empty($disposition))) {
+                if (!empty($disposition)) {
                     $encoded_name = $this->encodeHeader($this->secureHeader($name));
-                    if (preg_match('/[ \(\)<>@,;:\\"\/\[\]\?=]/', $encoded_name)) {
+                    if (preg_match('/[ ()<>@,;:"\/\[\]?=]/', $encoded_name)) {
                         $mime[] = sprintf(
                             'Content-Disposition: %s; filename="%s"%s',
                             $disposition,
                             $encoded_name,
                             static::$LE . static::$LE
                         );
+                    } elseif (!empty($encoded_name)) {
+                        $mime[] = sprintf(
+                            'Content-Disposition: %s; filename=%s%s',
+                            $disposition,
+                            $encoded_name,
+                            static::$LE . static::$LE
+                        );
                     } else {
-                        if (!empty($encoded_name)) {
-                            $mime[] = sprintf(
-                                'Content-Disposition: %s; filename=%s%s',
-                                $disposition,
-                                $encoded_name,
-                                static::$LE . static::$LE
-                            );
-                        } else {
-                            $mime[] = sprintf(
-                                'Content-Disposition: %s%s',
-                                $disposition,
-                                static::$LE . static::$LE
-                            );
-                        }
+                        $mime[] = sprintf(
+                            'Content-Disposition: %s%s',
+                            $disposition,
+                            static::$LE . static::$LE
+                        );
                     }
                 } else {
                     $mime[] = static::$LE;
@@ -2984,14 +3141,12 @@ class PHPMailer
      * @param string $path     The full path to the file
      * @param string $encoding The encoding to use; one of 'base64', '7bit', '8bit', 'binary', 'quoted-printable'
      *
-     * @throws Exception
-     *
      * @return string
      */
     protected function encodeFile($path, $encoding = self::ENCODING_BASE64)
     {
         try {
-            if (!static::isPermittedPath($path) || !file_exists($path)) {
+            if (!static::isPermittedPath($path) || !file_exists($path) || !is_readable($path)) {
                 throw new Exception($this->lang('file_open') . $path, self::STOP_CONTINUE);
             }
             $file_buffer = file_get_contents($path);
@@ -3003,7 +3158,10 @@ class PHPMailer
             return $file_buffer;
         } catch (Exception $exc) {
             $this->setError($exc->getMessage());
-
+            $this->edebug($exc->getMessage());
+            if ($this->exceptions) {
+                throw $exc;
+            }
             return '';
         }
     }
@@ -3015,6 +3173,8 @@ class PHPMailer
      * @param string $str      The text to encode
      * @param string $encoding The encoding to use; one of 'base64', '7bit', '8bit', 'binary', 'quoted-printable'
      *
+     * @throws Exception
+     *
      * @return string
      */
     public function encodeString($str, $encoding = self::ENCODING_BASE64)
@@ -3032,7 +3192,7 @@ class PHPMailer
             case static::ENCODING_8BIT:
                 $encoded = static::normalizeBreaks($str);
                 // Make sure it ends with a line break
-                if (substr($encoded, -(strlen(static::$LE))) != static::$LE) {
+                if (substr($encoded, -(strlen(static::$LE))) !== static::$LE) {
                     $encoded .= static::$LE;
                 }
                 break;
@@ -3044,6 +3204,9 @@ class PHPMailer
                 break;
             default:
                 $this->setError($this->lang('encoding') . $encoding);
+                if ($this->exceptions) {
+                    throw new Exception($this->lang('encoding') . $encoding);
+                }
                 break;
         }
 
@@ -3068,7 +3231,7 @@ class PHPMailer
                 if (!preg_match('/[\200-\377]/', $str)) {
                     // Can't use addslashes as we don't know the value of magic_quotes_sybase
                     $encoded = addcslashes($str, "\0..\37\177\\\"");
-                    if (($str == $encoded) and !preg_match('/[^A-Za-z0-9!#$%&\'*+\/=?^_`{|}~ -]/', $str)) {
+                    if (($str === $encoded) && !preg_match('/[^A-Za-z0-9!#$%&\'*+\/=?^_`{|}~ -]/', $str)) {
                         return $encoded;
                     }
 
@@ -3086,51 +3249,57 @@ class PHPMailer
                 break;
         }
 
-        //RFCs specify a maximum line length of 78 chars, however mail() will sometimes
-        //corrupt messages with headers longer than 65 chars. See #818
-        $lengthsub = 'mail' == $this->Mailer ? 13 : 0;
-        $maxlen = static::STD_LINE_LENGTH - $lengthsub;
-        // Try to select the encoding which should produce the shortest output
+        if ($this->has8bitChars($str)) {
+            $charset = $this->CharSet;
+        } else {
+            $charset = static::CHARSET_ASCII;
+        }
+
+        // Q/B encoding adds 8 chars and the charset ("` =?<charset>?[QB]?<content>?=`").
+        $overhead = 8 + strlen($charset);
+
+        if ('mail' === $this->Mailer) {
+            $maxlen = static::MAIL_MAX_LINE_LENGTH - $overhead;
+        } else {
+            $maxlen = static::MAX_LINE_LENGTH - $overhead;
+        }
+
+        // Select the encoding that produces the shortest output and/or prevents corruption.
         if ($matchcount > strlen($str) / 3) {
-            // More than a third of the content will need encoding, so B encoding will be most efficient
+            // More than 1/3 of the content needs encoding, use B-encode.
             $encoding = 'B';
-            //This calculation is:
-            // max line length
-            // - shorten to avoid mail() corruption
-            // - Q/B encoding char overhead ("` =?<charset>?[QB]?<content>?=`")
-            // - charset name length
-            $maxlen = static::STD_LINE_LENGTH - $lengthsub - 8 - strlen($this->CharSet);
-            if ($this->hasMultiBytes($str)) {
-                // Use a custom function which correctly encodes and wraps long
-                // multibyte strings without breaking lines within a character
-                $encoded = $this->base64EncodeWrapMB($str, "\n");
-            } else {
-                $encoded = base64_encode($str);
-                $maxlen -= $maxlen % 4;
-                $encoded = trim(chunk_split($encoded, $maxlen, "\n"));
-            }
-            $encoded = preg_replace('/^(.*)$/m', ' =?' . $this->CharSet . "?$encoding?\\1?=", $encoded);
         } elseif ($matchcount > 0) {
-            //1 or more chars need encoding, use Q-encode
+            // Less than 1/3 of the content needs encoding, use Q-encode.
             $encoding = 'Q';
-            //Recalc max line length for Q encoding - see comments on B encode
-            $maxlen = static::STD_LINE_LENGTH - $lengthsub - 8 - strlen($this->CharSet);
-            $encoded = $this->encodeQ($str, $position);
-            $encoded = $this->wrapText($encoded, $maxlen, true);
-            $encoded = str_replace('=' . static::$LE, "\n", trim($encoded));
-            $encoded = preg_replace('/^(.*)$/m', ' =?' . $this->CharSet . "?$encoding?\\1?=", $encoded);
         } elseif (strlen($str) > $maxlen) {
-            //No chars need encoding, but line is too long, so fold it
-            $encoded = trim($this->wrapText($str, $maxlen, false));
-            if ($str == $encoded) {
-                //Wrapping nicely didn't work, wrap hard instead
-                $encoded = trim(chunk_split($str, static::STD_LINE_LENGTH, static::$LE));
-            }
-            $encoded = str_replace(static::$LE, "\n", trim($encoded));
-            $encoded = preg_replace('/^(.*)$/m', ' \\1', $encoded);
+            // No encoding needed, but value exceeds max line length, use Q-encode to prevent corruption.
+            $encoding = 'Q';
         } else {
-            //No reformatting needed
-            return $str;
+            // No reformatting needed
+            $encoding = false;
+        }
+
+        switch ($encoding) {
+            case 'B':
+                if ($this->hasMultiBytes($str)) {
+                    // Use a custom function which correctly encodes and wraps long
+                    // multibyte strings without breaking lines within a character
+                    $encoded = $this->base64EncodeWrapMB($str, "\n");
+                } else {
+                    $encoded = base64_encode($str);
+                    $maxlen -= $maxlen % 4;
+                    $encoded = trim(chunk_split($encoded, $maxlen, "\n"));
+                }
+                $encoded = preg_replace('/^(.*)$/m', ' =?' . $charset . "?$encoding?\\1?=", $encoded);
+                break;
+            case 'Q':
+                $encoded = $this->encodeQ($str, $position);
+                $encoded = $this->wrapText($encoded, $maxlen, true);
+                $encoded = str_replace('=' . static::$LE, "\n", trim($encoded));
+                $encoded = preg_replace('/^(.*)$/m', ' =?' . $charset . "?$encoding?\\1?=", $encoded);
+                break;
+            default:
+                return $str;
         }
 
         return trim(static::normalizeBreaks($encoded));
@@ -3194,6 +3363,7 @@ class PHPMailer
         // Base64 has a 4:3 ratio
         $avgLength = floor($length * $ratio * .75);
 
+        $offset = 0;
         for ($i = 0; $i < $mb_length; $i += $offset) {
             $lookBack = 0;
             do {
@@ -3254,7 +3424,6 @@ class PHPMailer
             default:
                 // RFC 2047 section 5.1
                 // Replace every high ascii, control, =, ? and _ characters
-                /** @noinspection SuspiciousAssignmentsInspection */
                 $pattern = '\000-\011\013\014\016-\037\075\077\137\177-\377' . $pattern;
                 break;
         }
@@ -3262,7 +3431,7 @@ class PHPMailer
         if (preg_match_all("/[{$pattern}]/", $encoded, $matches)) {
             // If the string contains an '=', make sure it's the first thing we replace
             // so as to avoid double-encoding
-            $eqkey = array_search('=', $matches[0]);
+            $eqkey = array_search('=', $matches[0], true);
             if (false !== $eqkey) {
                 unset($matches[0][$eqkey]);
                 array_unshift($matches[0], '=');
@@ -3286,6 +3455,10 @@ class PHPMailer
      * @param string $encoding    File encoding (see $Encoding)
      * @param string $type        File extension (MIME) type
      * @param string $disposition Disposition to use
+     *
+     * @throws Exception
+     *
+     * @return bool True on successfully adding an attachment
      */
     public function addStringAttachment(
         $string,
@@ -3294,21 +3467,38 @@ class PHPMailer
         $type = '',
         $disposition = 'attachment'
     ) {
-        // If a MIME type is not specified, try to work it out from the file name
-        if ('' == $type) {
-            $type = static::filenameToType($filename);
-        }
-        // Append to $attachment array
-        $this->attachment[] = [
-            0 => $string,
-            1 => $filename,
-            2 => basename($filename),
-            3 => $encoding,
-            4 => $type,
-            5 => true, // isStringAttachment
-            6 => $disposition,
-            7 => 0,
-        ];
+        try {
+            // If a MIME type is not specified, try to work it out from the file name
+            if ('' === $type) {
+                $type = static::filenameToType($filename);
+            }
+
+            if (!$this->validateEncoding($encoding)) {
+                throw new Exception($this->lang('encoding') . $encoding);
+            }
+
+            // Append to $attachment array
+            $this->attachment[] = [
+                0 => $string,
+                1 => $filename,
+                2 => static::mb_pathinfo($filename, PATHINFO_BASENAME),
+                3 => $encoding,
+                4 => $type,
+                5 => true, // isStringAttachment
+                6 => $disposition,
+                7 => 0,
+            ];
+        } catch (Exception $exc) {
+            $this->setError($exc->getMessage());
+            $this->edebug($exc->getMessage());
+            if ($this->exceptions) {
+                throw $exc;
+            }
+
+            return false;
+        }
+
+        return true;
     }
 
     /**
@@ -3328,37 +3518,57 @@ class PHPMailer
      * @param string $type        File MIME type
      * @param string $disposition Disposition to use
      *
+     * @throws Exception
+     *
      * @return bool True on successfully adding an attachment
      */
-    public function addEmbeddedImage($path, $cid, $name = '', $encoding = self::ENCODING_BASE64, $type = '', $disposition = 'inline')
-    {
-        if (!static::isPermittedPath($path) || !@is_file($path)) {
-            $this->setError($this->lang('file_access') . $path);
+    public function addEmbeddedImage(
+        $path,
+        $cid,
+        $name = '',
+        $encoding = self::ENCODING_BASE64,
+        $type = '',
+        $disposition = 'inline'
+    ) {
+        try {
+            if (!static::isPermittedPath($path) || !@is_file($path) || !is_readable($path)) {
+                throw new Exception($this->lang('file_access') . $path, self::STOP_CONTINUE);
+            }
 
-            return false;
-        }
+            // If a MIME type is not specified, try to work it out from the file name
+            if ('' === $type) {
+                $type = static::filenameToType($path);
+            }
 
-        // If a MIME type is not specified, try to work it out from the file name
-        if ('' == $type) {
-            $type = static::filenameToType($path);
-        }
+            if (!$this->validateEncoding($encoding)) {
+                throw new Exception($this->lang('encoding') . $encoding);
+            }
 
-        $filename = basename($path);
-        if ('' == $name) {
-            $name = $filename;
-        }
+            $filename = (string) static::mb_pathinfo($path, PATHINFO_BASENAME);
+            if ('' === $name) {
+                $name = $filename;
+            }
 
-        // Append to $attachment array
-        $this->attachment[] = [
-            0 => $path,
-            1 => $filename,
-            2 => $name,
-            3 => $encoding,
-            4 => $type,
-            5 => false, // isStringAttachment
-            6 => $disposition,
-            7 => $cid,
-        ];
+            // Append to $attachment array
+            $this->attachment[] = [
+                0 => $path,
+                1 => $filename,
+                2 => $name,
+                3 => $encoding,
+                4 => $type,
+                5 => false, // isStringAttachment
+                6 => $disposition,
+                7 => $cid,
+            ];
+        } catch (Exception $exc) {
+            $this->setError($exc->getMessage());
+            $this->edebug($exc->getMessage());
+            if ($this->exceptions) {
+                throw $exc;
+            }
+
+            return false;
+        }
 
         return true;
     }
@@ -3378,6 +3588,8 @@ class PHPMailer
      * @param string $type        MIME type - will be used in preference to any automatically derived type
      * @param string $disposition Disposition to use
      *
+     * @throws Exception
+     *
      * @return bool True on successfully adding an attachment
      */
     public function addStringEmbeddedImage(
@@ -3388,27 +3600,63 @@ class PHPMailer
         $type = '',
         $disposition = 'inline'
     ) {
-        // If a MIME type is not specified, try to work it out from the name
-        if ('' == $type and !empty($name)) {
-            $type = static::filenameToType($name);
-        }
-
-        // Append to $attachment array
-        $this->attachment[] = [
-            0 => $string,
-            1 => $name,
-            2 => $name,
-            3 => $encoding,
-            4 => $type,
-            5 => true, // isStringAttachment
-            6 => $disposition,
-            7 => $cid,
-        ];
+        try {
+            // If a MIME type is not specified, try to work it out from the name
+            if ('' === $type && !empty($name)) {
+                $type = static::filenameToType($name);
+            }
+
+            if (!$this->validateEncoding($encoding)) {
+                throw new Exception($this->lang('encoding') . $encoding);
+            }
+
+            // Append to $attachment array
+            $this->attachment[] = [
+                0 => $string,
+                1 => $name,
+                2 => $name,
+                3 => $encoding,
+                4 => $type,
+                5 => true, // isStringAttachment
+                6 => $disposition,
+                7 => $cid,
+            ];
+        } catch (Exception $exc) {
+            $this->setError($exc->getMessage());
+            $this->edebug($exc->getMessage());
+            if ($this->exceptions) {
+                throw $exc;
+            }
+
+            return false;
+        }
 
         return true;
     }
 
     /**
+     * Validate encodings.
+     *
+     * @param string $encoding
+     *
+     * @return bool
+     */
+    protected function validateEncoding($encoding)
+    {
+        return in_array(
+            $encoding,
+            [
+                self::ENCODING_7BIT,
+                self::ENCODING_QUOTED_PRINTABLE,
+                self::ENCODING_BASE64,
+                self::ENCODING_8BIT,
+                self::ENCODING_BINARY,
+            ],
+            true
+        );
+    }
+
+    /**
      * Check if an embedded attachment is present with this cid.
      *
      * @param string $cid
@@ -3418,7 +3666,7 @@ class PHPMailer
     protected function cidExists($cid)
     {
         foreach ($this->attachment as $attachment) {
-            if ('inline' == $attachment[6] and $cid == $attachment[7]) {
+            if ('inline' === $attachment[6] && $cid === $attachment[7]) {
                 return true;
             }
         }
@@ -3434,7 +3682,7 @@ class PHPMailer
     public function inlineImageExists()
     {
         foreach ($this->attachment as $attachment) {
-            if ('inline' == $attachment[6]) {
+            if ('inline' === $attachment[6]) {
                 return true;
             }
         }
@@ -3450,7 +3698,7 @@ class PHPMailer
     public function attachmentExists()
     {
         foreach ($this->attachment as $attachment) {
-            if ('attachment' == $attachment[6]) {
+            if ('attachment' === $attachment[6]) {
                 return true;
             }
         }
@@ -3477,8 +3725,8 @@ class PHPMailer
     {
         $this->RecipientsQueue = array_filter(
             $this->RecipientsQueue,
-            function ($params) use ($kind) {
-                return $params[0] != $kind;
+            static function ($params) use ($kind) {
+                return $params[0] !== $kind;
             }
         );
     }
@@ -3564,7 +3812,7 @@ class PHPMailer
     protected function setError($msg)
     {
         ++$this->error_count;
-        if ('smtp' == $this->Mailer and null !== $this->smtp) {
+        if ('smtp' === $this->Mailer && null !== $this->smtp) {
             $lasterror = $this->smtp->getError();
             if (!empty($lasterror['error'])) {
                 $msg .= $this->lang('smtp_error') . $lasterror['error'];
@@ -3607,9 +3855,9 @@ class PHPMailer
         $result = '';
         if (!empty($this->Hostname)) {
             $result = $this->Hostname;
-        } elseif (isset($_SERVER) and array_key_exists('SERVER_NAME', $_SERVER)) {
+        } elseif (isset($_SERVER) && array_key_exists('SERVER_NAME', $_SERVER)) {
             $result = $_SERVER['SERVER_NAME'];
-        } elseif (function_exists('gethostname') and gethostname() !== false) {
+        } elseif (function_exists('gethostname') && gethostname() !== false) {
             $result = gethostname();
         } elseif (php_uname('n') !== false) {
             $result = php_uname('n');
@@ -3633,22 +3881,23 @@ class PHPMailer
     {
         //Simple syntax limits
         if (empty($host)
-            or !is_string($host)
-            or strlen($host) > 256
+            || !is_string($host)
+            || strlen($host) > 256
+            || !preg_match('/^([a-zA-Z\d.-]*|\[[a-fA-F\d:]+])$/', $host)
         ) {
             return false;
         }
         //Looks like a bracketed IPv6 address
-        if (trim($host, '[]') != $host) {
-            return (bool) filter_var(trim($host, '[]'), FILTER_VALIDATE_IP, FILTER_FLAG_IPV6);
+        if (strlen($host) > 2 && substr($host, 0, 1) === '[' && substr($host, -1, 1) === ']') {
+            return filter_var(substr($host, 1, -1), FILTER_VALIDATE_IP, FILTER_FLAG_IPV6) !== false;
         }
         //If removing all the dots results in a numeric string, it must be an IPv4 address.
         //Need to check this first because otherwise things like `999.0.0.0` are considered valid host names
         if (is_numeric(str_replace('.', '', $host))) {
             //Is it a valid IPv4 address?
-            return (bool) filter_var($host, FILTER_VALIDATE_IP, FILTER_FLAG_IPV4);
+            return filter_var($host, FILTER_VALIDATE_IP, FILTER_FLAG_IPV4) !== false;
         }
-        if (filter_var('http://' . $host, FILTER_VALIDATE_URL)) {
+        if (filter_var('http://' . $host, FILTER_VALIDATE_URL) !== false) {
             //Is it a syntactically valid hostname?
             return true;
         }
@@ -3666,11 +3915,11 @@ class PHPMailer
     protected function lang($key)
     {
         if (count($this->language) < 1) {
-            $this->setLanguage('en'); // set the default language
+            $this->setLanguage(); // set the default language
         }
 
         if (array_key_exists($key, $this->language)) {
-            if ('smtp_connect_failed' == $key) {
+            if ('smtp_connect_failed' === $key) {
                 //Include a link to troubleshooting docs on SMTP connection failure
                 //this is by far the biggest cause of support questions
                 //but it's usually not PHPMailer's fault.
@@ -3701,15 +3950,28 @@ class PHPMailer
      *
      * @param string      $name  Custom header name
      * @param string|null $value Header value
+     *
+     * @throws Exception
      */
     public function addCustomHeader($name, $value = null)
     {
-        if (null === $value) {
+        if (null === $value && strpos($name, ':') !== false) {
             // Value passed in as name:value
-            $this->CustomHeader[] = explode(':', $name, 2);
-        } else {
-            $this->CustomHeader[] = [$name, $value];
+            list($name, $value) = explode(':', $name, 2);
         }
+        $name = trim($name);
+        $value = trim($value);
+        //Ensure name is not empty, and that neither name nor value contain line breaks
+        if (empty($name) || strpbrk($name . $value, "\r\n") !== false) {
+            if ($this->exceptions) {
+                throw new Exception('Invalid header name or value');
+            }
+
+            return false;
+        }
+        $this->CustomHeader[] = [$name, $value];
+
+        return true;
     }
 
     /**
@@ -3736,36 +3998,45 @@ class PHPMailer
      * @param string        $message  HTML message string
      * @param string        $basedir  Absolute path to a base directory to prepend to relative paths to images
      * @param bool|callable $advanced Whether to use the internal HTML to text converter
-     *                                or your own custom converter @see PHPMailer::html2text()
+     *                                or your own custom converter @return string $message The transformed message Body
+     *
+     * @throws Exception
      *
-     * @return string $message The transformed message Body
+     * @see PHPMailer::html2text()
      */
     public function msgHTML($message, $basedir = '', $advanced = false)
     {
-        preg_match_all('/(src|background)=["\'](.*)["\']/Ui', $message, $images);
+        preg_match_all('/(?<!-)(src|background)=["\'](.*)["\']/Ui', $message, $images);
         if (array_key_exists(2, $images)) {
-            if (strlen($basedir) > 1 && '/' != substr($basedir, -1)) {
+            if (strlen($basedir) > 1 && '/' !== substr($basedir, -1)) {
                 // Ensure $basedir has a trailing /
                 $basedir .= '/';
             }
             foreach ($images[2] as $imgindex => $url) {
                 // Convert data URIs into embedded images
                 //e.g. "data:image/gif;base64,R0lGODlhAQABAAAAACH5BAEKAAEALAAAAAABAAEAAAICTAEAOw=="
+                $match = [];
                 if (preg_match('#^data:(image/(?:jpe?g|gif|png));?(base64)?,(.+)#', $url, $match)) {
-                    if (count($match) == 4 and static::ENCODING_BASE64 == $match[2]) {
+                    if (count($match) === 4 && static::ENCODING_BASE64 === $match[2]) {
                         $data = base64_decode($match[3]);
-                    } elseif ('' == $match[2]) {
+                    } elseif ('' === $match[2]) {
                         $data = rawurldecode($match[3]);
                     } else {
                         //Not recognised so leave it alone
                         continue;
                     }
-                    //Hash the decoded data, not the URL so that the same data-URI image used in multiple places
+                    //Hash the decoded data, not the URL, so that the same data-URI image used in multiple places
                     //will only be embedded once, even if it used a different encoding
-                    $cid = hash('sha256', $data) . '@phpmailer.0'; // RFC2392 S 2
+                    $cid = substr(hash('sha256', $data), 0, 32) . '@phpmailer.0'; // RFC2392 S 2
 
                     if (!$this->cidExists($cid)) {
-                        $this->addStringEmbeddedImage($data, $cid, 'embed' . $imgindex, static::ENCODING_BASE64, $match[1]);
+                        $this->addStringEmbeddedImage(
+                            $data,
+                            $cid,
+                            'embed' . $imgindex,
+                            static::ENCODING_BASE64,
+                            $match[1]
+                        );
                     }
                     $message = str_replace(
                         $images[0][$imgindex],
@@ -3777,22 +4048,23 @@ class PHPMailer
                 if (// Only process relative URLs if a basedir is provided (i.e. no absolute local paths)
                     !empty($basedir)
                     // Ignore URLs containing parent dir traversal (..)
-                    and (strpos($url, '..') === false)
+                    && (strpos($url, '..') === false)
                     // Do not change urls that are already inline images
-                    and 0 !== strpos($url, 'cid:')
+                    && 0 !== strpos($url, 'cid:')
                     // Do not change absolute URLs, including anonymous protocol
-                    and !preg_match('#^[a-z][a-z0-9+.-]*:?//#i', $url)
+                    && !preg_match('#^[a-z][a-z0-9+.-]*:?//#i', $url)
                 ) {
-                    $filename = basename($url);
+                    $filename = static::mb_pathinfo($url, PATHINFO_BASENAME);
                     $directory = dirname($url);
-                    if ('.' == $directory) {
+                    if ('.' === $directory) {
                         $directory = '';
                     }
-                    $cid = hash('sha256', $url) . '@phpmailer.0'; // RFC2392 S 2
-                    if (strlen($basedir) > 1 and '/' != substr($basedir, -1)) {
+                    // RFC2392 S 2
+                    $cid = substr(hash('sha256', $url), 0, 32) . '@phpmailer.0';
+                    if (strlen($basedir) > 1 && '/' !== substr($basedir, -1)) {
                         $basedir .= '/';
                     }
-                    if (strlen($directory) > 1 and '/' != substr($directory, -1)) {
+                    if (strlen($directory) > 1 && '/' !== substr($directory, -1)) {
                         $directory .= '/';
                     }
                     if ($this->addEmbeddedImage(
@@ -3812,7 +4084,7 @@ class PHPMailer
                 }
             }
         }
-        $this->isHTML(true);
+        $this->isHTML();
         // Convert all message body line breaks to LE, makes quoted-printable encoding work much better
         $this->Body = static::normalizeBreaks($message);
         $this->AltBody = static::normalizeBreaks($this->html2text($message, $advanced));
@@ -3850,7 +4122,7 @@ class PHPMailer
     public function html2text($html, $advanced = false)
     {
         if (is_callable($advanced)) {
-            return call_user_func($advanced, $html);
+            return $advanced($html);
         }
 
         return html_entity_decode(
@@ -4014,7 +4286,7 @@ class PHPMailer
      * Multi-byte-safe pathinfo replacement.
      * Drop-in replacement for pathinfo(), but multibyte- and cross-platform-safe.
      *
-     * @see    http://www.php.net/manual/en/function.pathinfo.php#107461
+     * @see http://www.php.net/manual/en/function.pathinfo.php#107461
      *
      * @param string     $path    A filename or path, does not need to exist as a file
      * @param int|string $options Either a PATHINFO_* constant,
@@ -4026,7 +4298,7 @@ class PHPMailer
     {
         $ret = ['dirname' => '', 'basename' => '', 'extension' => '', 'filename' => ''];
         $pathinfo = [];
-        if (preg_match('#^(.*?)[\\\\/]*(([^/\\\\]*?)(\.([^\.\\\\/]+?)|))[\\\\/\.]*$#im', $path, $pathinfo)) {
+        if (preg_match('#^(.*?)[\\\\/]*(([^/\\\\]*?)(\.([^.\\\\/]+?)|))[\\\\/.]*$#m', $path, $pathinfo)) {
             if (array_key_exists(1, $pathinfo)) {
                 $ret['dirname'] = $pathinfo[1];
             }
@@ -4063,9 +4335,9 @@ class PHPMailer
      * You should avoid this function - it's more verbose, less efficient, more error-prone and
      * harder to debug than setting properties directly.
      * Usage Example:
-     * `$mail->set('SMTPSecure', 'tls');`
+     * `$mail->set('SMTPSecure', static::ENCRYPTION_STARTTLS);`
      *   is the same as:
-     * `$mail->SMTPSecure = 'tls';`.
+     * `$mail->SMTPSecure = static::ENCRYPTION_STARTTLS;`.
      *
      * @param string $name  The property name to set
      * @param mixed  $value The value to set the property to
@@ -4112,7 +4384,7 @@ class PHPMailer
             $breaktype = static::$LE;
         }
         // Normalise to \n
-        $text = str_replace(["\r\n", "\r"], "\n", $text);
+        $text = str_replace([self::CRLF, "\r"], "\n", $text);
         // Now convert LE as needed
         if ("\n" !== $breaktype) {
             $text = str_replace("\n", $breaktype, $text);
@@ -4122,6 +4394,18 @@ class PHPMailer
     }
 
     /**
+     * Remove trailing breaks from a string.
+     *
+     * @param string $text
+     *
+     * @return string The text to remove breaks from
+     */
+    public static function stripTrailingWSP($text)
+    {
+        return rtrim($text, " \r\n\t");
+    }
+
+    /**
      * Return the current line break format string.
      *
      * @return string
@@ -4170,7 +4454,7 @@ class PHPMailer
         $len = strlen($txt);
         for ($i = 0; $i < $len; ++$i) {
             $ord = ord($txt[$i]);
-            if (((0x21 <= $ord) and ($ord <= 0x3A)) or $ord == 0x3C or ((0x3E <= $ord) and ($ord <= 0x7E))) {
+            if (((0x21 <= $ord) && ($ord <= 0x3A)) || $ord === 0x3C || ((0x3E <= $ord) && ($ord <= 0x7E))) {
                 $line .= $txt[$i];
             } else {
                 $line .= '=' . sprintf('%02X', $ord);
@@ -4201,7 +4485,7 @@ class PHPMailer
         $privKeyStr = !empty($this->DKIM_private_string) ?
             $this->DKIM_private_string :
             file_get_contents($this->DKIM_private);
-        if ('' != $this->DKIM_passphrase) {
+        if ('' !== $this->DKIM_passphrase) {
             $privKey = openssl_pkey_get_private($privKeyStr, $this->DKIM_passphrase);
         } else {
             $privKey = openssl_pkey_get_private($privKeyStr);
@@ -4221,7 +4505,7 @@ class PHPMailer
      * Uses the 'relaxed' algorithm from RFC6376 section 3.4.2.
      * Canonicalized headers should *always* use CRLF, regardless of mailer setting.
      *
-     * @see    https://tools.ietf.org/html/rfc6376#section-3.4.2
+     * @see https://tools.ietf.org/html/rfc6376#section-3.4.2
      *
      * @param string $signHeader Header
      *
@@ -4229,13 +4513,15 @@ class PHPMailer
      */
     public function DKIM_HeaderC($signHeader)
     {
-        //Unfold all header continuation lines
-        //Also collapses folded whitespace.
+        //Normalize breaks to CRLF (regardless of the mailer)
+        $signHeader = static::normalizeBreaks($signHeader, self::CRLF);
+        //Unfold header lines
         //Note PCRE \s is too broad a definition of whitespace; RFC5322 defines it as `[ \t]`
         //@see https://tools.ietf.org/html/rfc5322#section-2.2
         //That means this may break if you do something daft like put vertical tabs in your headers.
         $signHeader = preg_replace('/\r\n[ \t]+/', ' ', $signHeader);
-        $lines = explode("\r\n", $signHeader);
+        //Break headers out into an array
+        $lines = explode(self::CRLF, $signHeader);
         foreach ($lines as $key => $line) {
             //If the header is missing a :, skip it as it's invalid
             //This is likely to happen because the explode() above will also split
@@ -4246,16 +4532,16 @@ class PHPMailer
             list($heading, $value) = explode(':', $line, 2);
             //Lower-case header name
             $heading = strtolower($heading);
-            //Collapse white space within the value
-            $value = preg_replace('/[ \t]{2,}/', ' ', $value);
+            //Collapse white space within the value, also convert WSP to space
+            $value = preg_replace('/[ \t]+/', ' ', $value);
             //RFC6376 is slightly unclear here - it says to delete space at the *end* of each value
             //But then says to delete space before and after the colon.
             //Net result is the same as trimming both ends of the value.
-            //by elimination, the same applies to the field name
+            //By elimination, the same applies to the field name
             $lines[$key] = trim($heading, " \t") . ':' . trim($value, " \t");
         }
 
-        return implode("\r\n", $lines);
+        return implode(self::CRLF, $lines);
     }
 
     /**
@@ -4263,7 +4549,7 @@ class PHPMailer
      * Uses the 'simple' algorithm from RFC6376 section 3.4.3.
      * Canonicalized bodies should *always* use CRLF, regardless of mailer setting.
      *
-     * @see    https://tools.ietf.org/html/rfc6376#section-3.4.3
+     * @see https://tools.ietf.org/html/rfc6376#section-3.4.3
      *
      * @param string $body Message Body
      *
@@ -4272,13 +4558,13 @@ class PHPMailer
     public function DKIM_BodyC($body)
     {
         if (empty($body)) {
-            return "\r\n";
+            return self::CRLF;
         }
         // Normalize line endings to CRLF
-        $body = static::normalizeBreaks($body, "\r\n");
+        $body = static::normalizeBreaks($body, self::CRLF);
 
         //Reduce multiple trailing line breaks to a single one
-        return rtrim($body, "\r\n") . "\r\n";
+        return static::stripTrailingWSP($body) . self::CRLF;
     }
 
     /**
@@ -4288,109 +4574,143 @@ class PHPMailer
      * @param string $subject      Subject
      * @param string $body         Body
      *
+     * @throws Exception
+     *
      * @return string
      */
     public function DKIM_Add($headers_line, $subject, $body)
     {
         $DKIMsignatureType = 'rsa-sha256'; // Signature & hash algorithms
-        $DKIMcanonicalization = 'relaxed/simple'; // Canonicalization of header/body
+        $DKIMcanonicalization = 'relaxed/simple'; // Canonicalization methods of header & body
         $DKIMquery = 'dns/txt'; // Query method
-        $DKIMtime = time(); // Signature Timestamp = seconds since 00:00:00 - Jan 1, 1970 (UTC time zone)
-        $subject_header = "Subject: $subject";
-        $headers = explode(static::$LE, $headers_line);
-        $from_header = '';
-        $to_header = '';
-        $date_header = '';
-        $current = '';
-        $copiedHeaderFields = '';
-        $foundExtraHeaders = [];
-        $extraHeaderKeys = '';
-        $extraHeaderValues = '';
-        $extraCopyHeaderFields = '';
-        foreach ($headers as $header) {
-            if (strpos($header, 'From:') === 0) {
-                $from_header = $header;
-                $current = 'from_header';
-            } elseif (strpos($header, 'To:') === 0) {
-                $to_header = $header;
-                $current = 'to_header';
-            } elseif (strpos($header, 'Date:') === 0) {
-                $date_header = $header;
-                $current = 'date_header';
-            } elseif (!empty($this->DKIM_extraHeaders)) {
-                foreach ($this->DKIM_extraHeaders as $extraHeader) {
-                    if (strpos($header, $extraHeader . ':') === 0) {
-                        $headerValue = $header;
-                        foreach ($this->CustomHeader as $customHeader) {
-                            if ($customHeader[0] === $extraHeader) {
-                                $headerValue = trim($customHeader[0]) .
-                                               ': ' .
-                                               $this->encodeHeader(trim($customHeader[1]));
-                                break;
-                            }
+        $DKIMtime = time();
+        //Always sign these headers without being asked
+        //Recommended list from https://tools.ietf.org/html/rfc6376#section-5.4.1
+        $autoSignHeaders = [
+            'from',
+            'to',
+            'cc',
+            'date',
+            'subject',
+            'reply-to',
+            'message-id',
+            'content-type',
+            'mime-version',
+            'x-mailer',
+        ];
+        if (stripos($headers_line, 'Subject') === false) {
+            $headers_line .= 'Subject: ' . $subject . static::$LE;
+        }
+        $headerLines = explode(static::$LE, $headers_line);
+        $currentHeaderLabel = '';
+        $currentHeaderValue = '';
+        $parsedHeaders = [];
+        $headerLineIndex = 0;
+        $headerLineCount = count($headerLines);
+        foreach ($headerLines as $headerLine) {
+            $matches = [];
+            if (preg_match('/^([^ \t]*?)(?::[ \t]*)(.*)$/', $headerLine, $matches)) {
+                if ($currentHeaderLabel !== '') {
+                    //We were previously in another header; This is the start of a new header, so save the previous one
+                    $parsedHeaders[] = ['label' => $currentHeaderLabel, 'value' => $currentHeaderValue];
+                }
+                $currentHeaderLabel = $matches[1];
+                $currentHeaderValue = $matches[2];
+            } elseif (preg_match('/^[ \t]+(.*)$/', $headerLine, $matches)) {
+                //This is a folded continuation of the current header, so unfold it
+                $currentHeaderValue .= ' ' . $matches[1];
+            }
+            ++$headerLineIndex;
+            if ($headerLineIndex >= $headerLineCount) {
+                //This was the last line, so finish off this header
+                $parsedHeaders[] = ['label' => $currentHeaderLabel, 'value' => $currentHeaderValue];
+            }
+        }
+        $copiedHeaders = [];
+        $headersToSignKeys = [];
+        $headersToSign = [];
+        foreach ($parsedHeaders as $header) {
+            //Is this header one that must be included in the DKIM signature?
+            if (in_array(strtolower($header['label']), $autoSignHeaders, true)) {
+                $headersToSignKeys[] = $header['label'];
+                $headersToSign[] = $header['label'] . ': ' . $header['value'];
+                if ($this->DKIM_copyHeaderFields) {
+                    $copiedHeaders[] = $header['label'] . ':' . //Note no space after this, as per RFC
+                        str_replace('|', '=7C', $this->DKIM_QP($header['value']));
+                }
+                continue;
+            }
+            //Is this an extra custom header we've been asked to sign?
+            if (in_array($header['label'], $this->DKIM_extraHeaders, true)) {
+                //Find its value in custom headers
+                foreach ($this->CustomHeader as $customHeader) {
+                    if ($customHeader[0] === $header['label']) {
+                        $headersToSignKeys[] = $header['label'];
+                        $headersToSign[] = $header['label'] . ': ' . $header['value'];
+                        if ($this->DKIM_copyHeaderFields) {
+                            $copiedHeaders[] = $header['label'] . ':' . //Note no space after this, as per RFC
+                                str_replace('|', '=7C', $this->DKIM_QP($header['value']));
                         }
-                        $foundExtraHeaders[$extraHeader] = $headerValue;
-                        $current = '';
-                        break;
+                        //Skip straight to the next header
+                        continue 2;
                     }
                 }
-            } else {
-                if (!empty($$current) and strpos($header, ' =?') === 0) {
-                    $$current .= $header;
-                } else {
-                    $current = '';
-                }
             }
         }
-        foreach ($foundExtraHeaders as $key => $value) {
-            $extraHeaderKeys .= ':' . $key;
-            $extraHeaderValues .= $value . "\r\n";
-            if ($this->DKIM_copyHeaderFields) {
-                $extraCopyHeaderFields .= "\t|" . str_replace('|', '=7C', $this->DKIM_QP($value)) . ";\r\n";
+        $copiedHeaderFields = '';
+        if ($this->DKIM_copyHeaderFields && count($copiedHeaders) > 0) {
+            //Assemble a DKIM 'z' tag
+            $copiedHeaderFields = ' z=';
+            $first = true;
+            foreach ($copiedHeaders as $copiedHeader) {
+                if (!$first) {
+                    $copiedHeaderFields .= static::$LE . ' |';
+                }
+                //Fold long values
+                if (strlen($copiedHeader) > self::STD_LINE_LENGTH - 3) {
+                    $copiedHeaderFields .= substr(
+                        chunk_split($copiedHeader, self::STD_LINE_LENGTH - 3, static::$LE . self::FWS),
+                        0,
+                        -strlen(static::$LE . self::FWS)
+                    );
+                } else {
+                    $copiedHeaderFields .= $copiedHeader;
+                }
+                $first = false;
             }
+            $copiedHeaderFields .= ';' . static::$LE;
         }
-        if ($this->DKIM_copyHeaderFields) {
-            $from = str_replace('|', '=7C', $this->DKIM_QP($from_header));
-            $to = str_replace('|', '=7C', $this->DKIM_QP($to_header));
-            $date = str_replace('|', '=7C', $this->DKIM_QP($date_header));
-            $subject = str_replace('|', '=7C', $this->DKIM_QP($subject_header));
-            $copiedHeaderFields = "\tz=$from\r\n" .
-                                  "\t|$to\r\n" .
-                                  "\t|$date\r\n" .
-                                  "\t|$subject;\r\n" .
-                                  $extraCopyHeaderFields;
-        }
+        $headerKeys = ' h=' . implode(':', $headersToSignKeys) . ';' . static::$LE;
+        $headerValues = implode(static::$LE, $headersToSign);
         $body = $this->DKIM_BodyC($body);
-        $DKIMlen = strlen($body); // Length of body
         $DKIMb64 = base64_encode(pack('H*', hash('sha256', $body))); // Base64 of packed binary SHA-256 hash of body
-        if ('' == $this->DKIM_identity) {
-            $ident = '';
-        } else {
-            $ident = ' i=' . $this->DKIM_identity . ';';
-        }
-        $dkimhdrs = 'DKIM-Signature: v=1; a=' .
-            $DKIMsignatureType . '; q=' .
-            $DKIMquery . '; l=' .
-            $DKIMlen . '; s=' .
-            $this->DKIM_selector .
-            ";\r\n" .
-            "\tt=" . $DKIMtime . '; c=' . $DKIMcanonicalization . ";\r\n" .
-            "\th=From:To:Date:Subject" . $extraHeaderKeys . ";\r\n" .
-            "\td=" . $this->DKIM_domain . ';' . $ident . "\r\n" .
+        $ident = '';
+        if ('' !== $this->DKIM_identity) {
+            $ident = ' i=' . $this->DKIM_identity . ';' . static::$LE;
+        }
+        //The DKIM-Signature header is included in the signature *except for* the value of the `b` tag
+        //which is appended after calculating the signature
+        //https://tools.ietf.org/html/rfc6376#section-3.5
+        $dkimSignatureHeader = 'DKIM-Signature: v=1;' .
+            ' d=' . $this->DKIM_domain . ';' .
+            ' s=' . $this->DKIM_selector . ';' . static::$LE .
+            ' a=' . $DKIMsignatureType . ';' .
+            ' q=' . $DKIMquery . ';' .
+            ' t=' . $DKIMtime . ';' .
+            ' c=' . $DKIMcanonicalization . ';' . static::$LE .
+            $headerKeys .
+            $ident .
             $copiedHeaderFields .
-            "\tbh=" . $DKIMb64 . ";\r\n" .
-            "\tb=";
-        $toSign = $this->DKIM_HeaderC(
-            $from_header . "\r\n" .
-            $to_header . "\r\n" .
-            $date_header . "\r\n" .
-            $subject_header . "\r\n" .
-            $extraHeaderValues .
-            $dkimhdrs
+            ' bh=' . $DKIMb64 . ';' . static::$LE .
+            ' b=';
+        //Canonicalize the set of headers
+        $canonicalizedHeaders = $this->DKIM_HeaderC(
+            $headerValues . static::$LE . $dkimSignatureHeader
         );
-        $signed = $this->DKIM_Sign($toSign);
+        $signature = $this->DKIM_Sign($canonicalizedHeaders);
+        $signature = trim(chunk_split($signature, self::STD_LINE_LENGTH - 3, static::$LE . self::FWS));
 
-        return static::normalizeBreaks($dkimhdrs . $signed) . static::$LE;
+        return static::normalizeBreaks($dkimSignatureHeader . $signature);
     }
 
     /**
@@ -4475,7 +4795,7 @@ class PHPMailer
      */
     protected function doCallback($isSent, $to, $cc, $bcc, $subject, $body, $from, $extra)
     {
-        if (!empty($this->action_function) and is_callable($this->action_function)) {
+        if (!empty($this->action_function) && is_callable($this->action_function)) {
             call_user_func($this->action_function, $isSent, $to, $cc, $bcc, $subject, $body, $from, $extra);
         }
     }
@@ -4492,8 +4812,6 @@ class PHPMailer
 
     /**
      * Set an OAuth instance.
-     *
-     * @param OAuth $oauth
      */
     public function setOAuth(OAuth $oauth)
     {
diff --git a/lib/PHPMailer/PHPMailer/SMTP.php b/lib/PHPMailer/PHPMailer/SMTP.php
index da85442bf..1e38ba7da 100644
--- a/lib/PHPMailer/PHPMailer/SMTP.php
+++ b/lib/PHPMailer/PHPMailer/SMTP.php
@@ -9,7 +9,7 @@
  * @author    Jim Jagielski (jimjag) <jimjag@gmail.com>
  * @author    Andy Prevost (codeworxtech) <codeworxtech@users.sourceforge.net>
  * @author    Brent R. Matzelle (original founder)
- * @copyright 2012 - 2017 Marcus Bointon
+ * @copyright 2012 - 2019 Marcus Bointon
  * @copyright 2010 - 2012 Jim Jagielski
  * @copyright 2004 - 2009 Andy Prevost
  * @license   http://www.gnu.org/copyleft/lesser.html GNU Lesser General Public License
@@ -24,8 +24,8 @@ namespace PHPMailer\PHPMailer;
  * PHPMailer RFC821 SMTP email transport class.
  * Implements RFC 821 SMTP commands and provides some utility methods for sending mail to an SMTP server.
  *
- * @author  Chris Ryan
- * @author  Marcus Bointon <phpmailer@synchromedia.co.uk>
+ * @author Chris Ryan
+ * @author Marcus Bointon <phpmailer@synchromedia.co.uk>
  */
 class SMTP
 {
@@ -34,7 +34,7 @@ class SMTP
      *
      * @var string
      */
-    const VERSION = '6.0.7';
+    const VERSION = '6.1.5';
 
     /**
      * SMTP line break constant.
@@ -51,34 +51,57 @@ class SMTP
     const DEFAULT_PORT = 25;
 
     /**
-     * The maximum line length allowed by RFC 2822 section 2.1.1.
+     * The maximum line length allowed by RFC 5321 section 4.5.3.1.6,
+     * *excluding* a trailing CRLF break.
+     *
+     * @see https://tools.ietf.org/html/rfc5321#section-4.5.3.1.6
      *
      * @var int
      */
     const MAX_LINE_LENGTH = 998;
 
     /**
+     * The maximum line length allowed for replies in RFC 5321 section 4.5.3.1.5,
+     * *including* a trailing CRLF line break.
+     *
+     * @see https://tools.ietf.org/html/rfc5321#section-4.5.3.1.5
+     *
+     * @var int
+     */
+    const MAX_REPLY_LENGTH = 512;
+
+    /**
      * Debug level for no output.
+     *
+     * @var int
      */
     const DEBUG_OFF = 0;
 
     /**
      * Debug level to show client -> server messages.
+     *
+     * @var int
      */
     const DEBUG_CLIENT = 1;
 
     /**
      * Debug level to show client -> server and server -> client messages.
+     *
+     * @var int
      */
     const DEBUG_SERVER = 2;
 
     /**
      * Debug level to show connection status, client -> server and server -> client messages.
+     *
+     * @var int
      */
     const DEBUG_CONNECTION = 3;
 
     /**
      * Debug level to show all messages.
+     *
+     * @var int
      */
     const DEBUG_LOWLEVEL = 4;
 
@@ -197,7 +220,7 @@ class SMTP
      *
      * @var string|null
      */
-    protected $helo_rply = null;
+    protected $helo_rply;
 
     /**
      * The set of SMTP extensions sent in reply to EHLO command.
@@ -209,7 +232,7 @@ class SMTP
      *
      * @var array|null
      */
-    protected $server_caps = null;
+    protected $server_caps;
 
     /**
      * The most recent reply received from the server.
@@ -239,7 +262,7 @@ class SMTP
             return;
         }
         //Avoid clash with built-in function names
-        if (!in_array($this->Debugoutput, ['error_log', 'html', 'echo']) and is_callable($this->Debugoutput)) {
+        if (is_callable($this->Debugoutput) && !in_array($this->Debugoutput, ['error_log', 'html', 'echo'])) {
             call_user_func($this->Debugoutput, $str, $level);
 
             return;
@@ -260,12 +283,12 @@ class SMTP
             case 'echo':
             default:
                 //Normalize line breaks
-                $str = preg_replace('/\r\n|\r/ms', "\n", $str);
+                $str = preg_replace('/\r\n|\r/m', "\n", $str);
                 echo gmdate('Y-m-d H:i:s'),
                 "\t",
                     //Trim trailing space
                 trim(
-                //Indent for readability, except for trailing break
+                    //Indent for readability, except for trailing break
                     str_replace(
                         "\n",
                         "\n                   \t                  ",
@@ -348,7 +371,7 @@ class SMTP
                 'Failed to connect to server',
                 '',
                 (string) $errno,
-                (string) $errstr
+                $errstr
             );
             $this->edebug(
                 'SMTP ERROR: ' . $this->error['error']
@@ -361,10 +384,10 @@ class SMTP
         $this->edebug('Connection: opened', self::DEBUG_CONNECTION);
         // SMTP server can take longer to respond, give longer timeout for first read
         // Windows does not have support for this timeout function
-        if (substr(PHP_OS, 0, 3) != 'WIN') {
-            $max = ini_get('max_execution_time');
+        if (strpos(PHP_OS, 'WIN') !== 0) {
+            $max = (int) ini_get('max_execution_time');
             // Don't bother if unlimited
-            if (0 != $max and $timeout > $max) {
+            if (0 !== $max && $timeout > $max) {
                 @set_time_limit($timeout);
             }
             stream_set_timeout($this->smtp_conn, $timeout, 0);
@@ -444,14 +467,14 @@ class SMTP
                 return false;
             }
 
-            $this->edebug('Auth method requested: ' . ($authtype ? $authtype : 'UNSPECIFIED'), self::DEBUG_LOWLEVEL);
+            $this->edebug('Auth method requested: ' . ($authtype ?: 'UNSPECIFIED'), self::DEBUG_LOWLEVEL);
             $this->edebug(
                 'Auth methods available on the server: ' . implode(',', $this->server_caps['AUTH']),
                 self::DEBUG_LOWLEVEL
             );
 
             //If we have requested a specific auth type, check the server supports it before trying others
-            if (null !== $authtype and !in_array($authtype, $this->server_caps['AUTH'])) {
+            if (null !== $authtype && !in_array($authtype, $this->server_caps['AUTH'], true)) {
                 $this->edebug('Requested auth method not available: ' . $authtype, self::DEBUG_LOWLEVEL);
                 $authtype = null;
             }
@@ -460,7 +483,7 @@ class SMTP
                 //If no auth mechanism is specified, attempt to use these, in this order
                 //Try CRAM-MD5 first as it's more secure than the others
                 foreach (['CRAM-MD5', 'LOGIN', 'PLAIN', 'XOAUTH2'] as $method) {
-                    if (in_array($method, $this->server_caps['AUTH'])) {
+                    if (in_array($method, $this->server_caps['AUTH'], true)) {
                         $authtype = $method;
                         break;
                     }
@@ -470,10 +493,10 @@ class SMTP
 
                     return false;
                 }
-                self::edebug('Auth method selected: ' . $authtype, self::DEBUG_LOWLEVEL);
+                $this->edebug('Auth method selected: ' . $authtype, self::DEBUG_LOWLEVEL);
             }
 
-            if (!in_array($authtype, $this->server_caps['AUTH'])) {
+            if (!in_array($authtype, $this->server_caps['AUTH'], true)) {
                 $this->setError("The requested authentication method \"$authtype\" is not supported by the server");
 
                 return false;
@@ -663,13 +686,13 @@ class SMTP
 
         $field = substr($lines[0], 0, strpos($lines[0], ':'));
         $in_headers = false;
-        if (!empty($field) and strpos($field, ' ') === false) {
+        if (!empty($field) && strpos($field, ' ') === false) {
             $in_headers = true;
         }
 
         foreach ($lines as $line) {
             $lines_out = [];
-            if ($in_headers and $line == '') {
+            if ($in_headers && $line === '') {
                 $in_headers = false;
             }
             //Break this line up into several smaller lines if it's too long
@@ -700,7 +723,7 @@ class SMTP
             //Send the lines to the server
             foreach ($lines_out as $line_out) {
                 //RFC2821 section 4.5.2
-                if (!empty($line_out) and $line_out[0] == '.') {
+                if (!empty($line_out) && $line_out[0] === '.') {
                     $line_out = '.' . $line_out;
                 }
                 $this->client_send($line_out . static::LE, 'DATA');
@@ -710,7 +733,7 @@ class SMTP
         //Message data has been sent, complete the command
         //Increase timelimit for end of DATA command
         $savetimelimit = $this->Timelimit;
-        $this->Timelimit = $this->Timelimit * 2;
+        $this->Timelimit *= 2;
         $result = $this->sendCommand('DATA END', '.', 250);
         $this->recordLastTransactionID();
         //Restore timelimit
@@ -745,7 +768,7 @@ class SMTP
      *
      * @return bool
      *
-     * @see    hello()
+     * @see hello()
      */
     protected function sendHello($hello, $host)
     {
@@ -838,7 +861,7 @@ class SMTP
     {
         $noerror = $this->sendCommand('QUIT', 'QUIT', 221);
         $err = $this->error; //Save any error
-        if ($noerror or $close_on_error) {
+        if ($noerror || $close_on_error) {
             $this->close();
             $this->error = $err; //Restore any error from the quit command
         }
@@ -853,14 +876,35 @@ class SMTP
      * Implements from RFC 821: RCPT <SP> TO:<forward-path> <CRLF>.
      *
      * @param string $address The address the message is being sent to
+     * @param string $dsn     Comma separated list of DSN notifications. NEVER, SUCCESS, FAILURE
+     *                        or DELAY. If you specify NEVER all other notifications are ignored.
      *
      * @return bool
      */
-    public function recipient($address)
+    public function recipient($address, $dsn = '')
     {
+        if (empty($dsn)) {
+            $rcpt = 'RCPT TO:<' . $address . '>';
+        } else {
+            $dsn = strtoupper($dsn);
+            $notify = [];
+
+            if (strpos($dsn, 'NEVER') !== false) {
+                $notify[] = 'NEVER';
+            } else {
+                foreach (['SUCCESS', 'FAILURE', 'DELAY'] as $value) {
+                    if (strpos($dsn, $value) !== false) {
+                        $notify[] = $value;
+                    }
+                }
+            }
+
+            $rcpt = 'RCPT TO:<' . $address . '> NOTIFY=' . implode(',', $notify);
+        }
+
         return $this->sendCommand(
             'RCPT TO',
-            'RCPT TO:<' . $address . '>',
+            $rcpt,
             [250, 251]
         );
     }
@@ -894,7 +938,7 @@ class SMTP
             return false;
         }
         //Reject line breaks in all commands
-        if (strpos($commandstring, "\n") !== false or strpos($commandstring, "\r") !== false) {
+        if ((strpos($commandstring, "\n") !== false) || (strpos($commandstring, "\r") !== false)) {
             $this->setError("Command '$command' contained line breaks");
 
             return false;
@@ -904,8 +948,8 @@ class SMTP
         $this->last_reply = $this->get_lines();
         // Fetch SMTP code and possible error code explanation
         $matches = [];
-        if (preg_match('/^([0-9]{3})[ -](?:([0-9]\\.[0-9]\\.[0-9]) )?/', $this->last_reply, $matches)) {
-            $code = $matches[1];
+        if (preg_match('/^([\d]{3})[ -](?:([\d]\\.[\d]\\.[\d]{1,2}) )?/', $this->last_reply, $matches)) {
+            $code = (int) $matches[1];
             $code_ex = (count($matches) > 2 ? $matches[2] : null);
             // Cut off error code from each response line
             $detail = preg_replace(
@@ -916,14 +960,14 @@ class SMTP
             );
         } else {
             // Fall back to simple parsing if regex fails
-            $code = substr($this->last_reply, 0, 3);
+            $code = (int) substr($this->last_reply, 0, 3);
             $code_ex = null;
             $detail = substr($this->last_reply, 4);
         }
 
         $this->edebug('SERVER -> CLIENT: ' . $this->last_reply, self::DEBUG_SERVER);
 
-        if (!in_array($code, (array) $expect)) {
+        if (!in_array($code, (array) $expect, true)) {
             $this->setError(
                 "$command command failed",
                 $detail,
@@ -1014,9 +1058,9 @@ class SMTP
     {
         //If SMTP transcripts are left enabled, or debug output is posted online
         //it can leak credentials, so hide credentials in all but lowest level
-        if (self::DEBUG_LOWLEVEL > $this->do_debug and
+        if (self::DEBUG_LOWLEVEL > $this->do_debug &&
             in_array($command, ['User & Password', 'Username', 'Password'], true)) {
-            $this->edebug('CLIENT -> SERVER: <credentials hidden>', self::DEBUG_CLIENT);
+            $this->edebug('CLIENT -> SERVER: [credentials hidden]', self::DEBUG_CLIENT);
         } else {
             $this->edebug('CLIENT -> SERVER: ' . $data, self::DEBUG_CLIENT);
         }
@@ -1062,7 +1106,7 @@ class SMTP
      *
      * @param string $name Name of SMTP extension or 'HELO'|'EHLO'
      *
-     * @return mixed
+     * @return string|bool|null
      */
     public function getServerExt($name)
     {
@@ -1073,10 +1117,10 @@ class SMTP
         }
 
         if (!array_key_exists($name, $this->server_caps)) {
-            if ('HELO' == $name) {
+            if ('HELO' === $name) {
                 return $this->server_caps['EHLO'];
             }
-            if ('EHLO' == $name || array_key_exists('EHLO', $this->server_caps)) {
+            if ('EHLO' === $name || array_key_exists('EHLO', $this->server_caps)) {
                 return false;
             }
             $this->setError('HELO handshake was used; No information about server extensions available');
@@ -1120,7 +1164,7 @@ class SMTP
         }
         $selR = [$this->smtp_conn];
         $selW = null;
-        while (is_resource($this->smtp_conn) and !feof($this->smtp_conn)) {
+        while (is_resource($this->smtp_conn) && !feof($this->smtp_conn)) {
             //Must pass vars in here as params are by reference
             if (!stream_select($selR, $selW, $selW, $this->Timelimit)) {
                 $this->edebug(
@@ -1130,13 +1174,13 @@ class SMTP
                 break;
             }
             //Deliberate noise suppression - errors are handled afterwards
-            $str = @fgets($this->smtp_conn, 515);
+            $str = @fgets($this->smtp_conn, self::MAX_REPLY_LENGTH);
             $this->edebug('SMTP INBOUND: "' . trim($str) . '"', self::DEBUG_LOWLEVEL);
             $data .= $str;
             // If response is only 3 chars (not valid, but RFC5321 S4.2 says it must be handled),
-            // or 4th character is a space, we are done reading, break the loop,
-            // string array access is a micro-optimisation over strlen
-            if (!isset($str[3]) or (isset($str[3]) and $str[3] == ' ')) {
+            // or 4th character is a space or a line break char, we are done reading, break the loop.
+            // String array access is a significant micro-optimisation over strlen
+            if (!isset($str[3]) || $str[3] === ' ' || $str[3] === "\r" || $str[3] === "\n") {
                 break;
             }
             // Timed-out? Log and break
@@ -1149,7 +1193,7 @@ class SMTP
                 break;
             }
             // Now check if reads took too long
-            if ($endtime and time() > $endtime) {
+            if ($endtime && time() > $endtime) {
                 $this->edebug(
                     'SMTP -> get_lines(): timelimit reached (' .
                     $this->Timelimit . ' sec)',
@@ -1289,7 +1333,7 @@ class SMTP
      * If no reply has been received yet, it will return null.
      * If no pattern was matched, it will return false.
      *
-     * @return bool|null|string
+     * @return bool|string|null
      */
     protected function recordLastTransactionID()
     {
@@ -1300,6 +1344,7 @@ class SMTP
         } else {
             $this->last_smtp_transaction_id = false;
             foreach ($this->smtp_transaction_id_patterns as $smtp_transaction_id_pattern) {
+                $matches = [];
                 if (preg_match($smtp_transaction_id_pattern, $reply, $matches)) {
                     $this->last_smtp_transaction_id = trim($matches[1]);
                     break;
@@ -1315,7 +1360,7 @@ class SMTP
      * If no reply has been received yet, it will return null.
      * If no pattern was matched, it will return false.
      *
-     * @return bool|null|string
+     * @return bool|string|null
      *
      * @see recordLastTransactionID()
      */