Update PHPMailer

lib/phpmailer/DSNConfigurator.php

@@ -0,0 +1,247 @@
+<?php
+
+/**
+ * PHPMailer - PHP email creation and transport class.
+ * PHP Version 5.5.
+ *
+ * @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 - 2023 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
+ * @note      This program is distributed in the hope that it will be useful - WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.
+ */
+
+namespace PHPMailer\PHPMailer;
+
+/**
+ * Configure PHPMailer with DSN string.
+ *
+ * @see https://en.wikipedia.org/wiki/Data_source_name
+ *
+ * @author Oleg Voronkovich <oleg-voronkovich@yandex.ru>
+ */
+class DSNConfigurator
+{
+    /**
+     * Create new PHPMailer instance configured by DSN.
+     *
+     * @param string $dsn        DSN
+     * @param bool   $exceptions Should we throw external exceptions?
+     *
+     * @return PHPMailer
+     */
+    public static function mailer($dsn, $exceptions = null)
+    {
+        static $configurator = null;
+
+        if (null === $configurator) {
+            $configurator = new DSNConfigurator();
+        }
+
+        return $configurator->configure(new PHPMailer($exceptions), $dsn);
+    }
+
+    /**
+     * Configure PHPMailer instance with DSN string.
+     *
+     * @param PHPMailer $mailer PHPMailer instance
+     * @param string    $dsn    DSN
+     *
+     * @return PHPMailer
+     */
+    public function configure(PHPMailer $mailer, $dsn)
+    {
+        $config = $this->parseDSN($dsn);
+
+        $this->applyConfig($mailer, $config);
+
+        return $mailer;
+    }
+
+    /**
+     * Parse DSN string.
+     *
+     * @param string $dsn DSN
+     *
+     * @throws Exception If DSN is malformed
+     *
+     * @return array Configuration
+     */
+    private function parseDSN($dsn)
+    {
+        $config = $this->parseUrl($dsn);
+
+        if (false === $config || !isset($config['scheme']) || !isset($config['host'])) {
+            throw new Exception(
+                sprintf('Malformed DSN: "%s".', $dsn)
+            );
+        }
+
+        if (isset($config['query'])) {
+            parse_str($config['query'], $config['query']);
+        }
+
+        return $config;
+    }
+
+    /**
+     * Apply configuration to mailer.
+     *
+     * @param PHPMailer $mailer PHPMailer instance
+     * @param array     $config Configuration
+     *
+     * @throws Exception If scheme is invalid
+     */
+    private function applyConfig(PHPMailer $mailer, $config)
+    {
+        switch ($config['scheme']) {
+            case 'mail':
+                $mailer->isMail();
+                break;
+            case 'sendmail':
+                $mailer->isSendmail();
+                break;
+            case 'qmail':
+                $mailer->isQmail();
+                break;
+            case 'smtp':
+            case 'smtps':
+                $mailer->isSMTP();
+                $this->configureSMTP($mailer, $config);
+                break;
+            default:
+                throw new Exception(
+                    sprintf(
+                        'Invalid scheme: "%s". Allowed values: "mail", "sendmail", "qmail", "smtp", "smtps".',
+                        $config['scheme']
+                    )
+                );
+        }
+
+        if (isset($config['query'])) {
+            $this->configureOptions($mailer, $config['query']);
+        }
+    }
+
+    /**
+     * Configure SMTP.
+     *
+     * @param PHPMailer $mailer PHPMailer instance
+     * @param array     $config Configuration
+     */
+    private function configureSMTP($mailer, $config)
+    {
+        $isSMTPS = 'smtps' === $config['scheme'];
+
+        if ($isSMTPS) {
+            $mailer->SMTPSecure = PHPMailer::ENCRYPTION_STARTTLS;
+        }
+
+        $mailer->Host = $config['host'];
+
+        if (isset($config['port'])) {
+            $mailer->Port = $config['port'];
+        } elseif ($isSMTPS) {
+            $mailer->Port = SMTP::DEFAULT_SECURE_PORT;
+        }
+
+        $mailer->SMTPAuth = isset($config['user']) || isset($config['pass']);
+
+        if (isset($config['user'])) {
+            $mailer->Username = $config['user'];
+        }
+
+        if (isset($config['pass'])) {
+            $mailer->Password = $config['pass'];
+        }
+    }
+
+    /**
+     * Configure options.
+     *
+     * @param PHPMailer $mailer  PHPMailer instance
+     * @param array     $options Options
+     *
+     * @throws Exception If option is unknown
+     */
+    private function configureOptions(PHPMailer $mailer, $options)
+    {
+        $allowedOptions = get_object_vars($mailer);
+
+        unset($allowedOptions['Mailer']);
+        unset($allowedOptions['SMTPAuth']);
+        unset($allowedOptions['Username']);
+        unset($allowedOptions['Password']);
+        unset($allowedOptions['Hostname']);
+        unset($allowedOptions['Port']);
+        unset($allowedOptions['ErrorInfo']);
+
+        $allowedOptions = \array_keys($allowedOptions);
+
+        foreach ($options as $key => $value) {
+            if (!in_array($key, $allowedOptions)) {
+                throw new Exception(
+                    sprintf(
+                        'Unknown option: "%s". Allowed values: "%s"',
+                        $key,
+                        implode('", "', $allowedOptions)
+                    )
+                );
+            }
+
+            switch ($key) {
+                case 'AllowEmpty':
+                case 'SMTPAutoTLS':
+                case 'SMTPKeepAlive':
+                case 'SingleTo':
+                case 'UseSendmailOptions':
+                case 'do_verp':
+                case 'DKIM_copyHeaderFields':
+                    $mailer->$key = (bool) $value;
+                    break;
+                case 'Priority':
+                case 'SMTPDebug':
+                case 'WordWrap':
+                    $mailer->$key = (int) $value;
+                    break;
+                default:
+                    $mailer->$key = $value;
+                    break;
+            }
+        }
+    }
+
+    /**
+     * Parse a URL.
+     * Wrapper for the built-in parse_url function to work around a bug in PHP 5.5.
+     *
+     * @param string $url URL
+     *
+     * @return array|false
+     */
+    protected function parseUrl($url)
+    {
+        if (\PHP_VERSION_ID >= 50600 || false === strpos($url, '?')) {
+            return parse_url($url);
+        }
+
+        $chunks = explode('?', $url);
+        if (is_array($chunks)) {
+            $result = parse_url($chunks[0]);
+            if (is_array($result)) {
+                $result['query'] = $chunks[1];
+            }
+            return $result;
+        }
+
+        return false;
+    }
+}

lib/phpmailer/Exception.php

@@ -1,4 +1,5 @@
 <?php
+
 /**
  * PHPMailer Exception class.
  * PHP Version 5.5.
@@ -9,7 +10,7 @@
  * @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 - 2020 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
@@ -18,6 +19,8 @@
  * FITNESS FOR A PARTICULAR PURPOSE.
  */
 
+namespace PHPMailer\PHPMailer;
+
 /**
  * PHPMailer exception handler.
  *
@@ -32,6 +35,6 @@ class Exception extends \Exception
      */
     public function errorMessage()
     {
-        return '<strong>' . htmlspecialchars($this->getMessage()) . "</strong><br />\n";
+        return '<strong>' . htmlspecialchars($this->getMessage(), ENT_COMPAT | ENT_HTML401) . "</strong><br />\n";
     }
 }

lib/phpmailer/OAuth.php

@@ -1,4 +1,5 @@
 <?php
+
 /**
  * PHPMailer - PHP email creation and transport class.
  * PHP Version 5.5.
@@ -9,7 +10,7 @@
  * @author    Jim Jagielski (jimjag) <jimjag@gmail.com>
  * @author    Andy Prevost (codeworxtech) <codeworxtech@users.sourceforge.net>
  * @author    Brent R. Matzelle (original founder)
- * @copyright 2012 - 2015 Marcus Bointon
+ * @copyright 2012 - 2020 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
@@ -18,6 +19,8 @@
  * FITNESS FOR A PARTICULAR PURPOSE.
  */
 
+namespace PHPMailer\PHPMailer;
+
 use League\OAuth2\Client\Grant\RefreshToken;
 use League\OAuth2\Client\Provider\AbstractProvider;
 use League\OAuth2\Client\Token\AccessToken;
@@ -30,7 +33,7 @@ use League\OAuth2\Client\Token\AccessToken;
  *
  * @author  Marcus Bointon (Synchro/coolbru) <phpmailer@synchromedia.co.uk>
  */
-class OAuth
+class OAuth implements OAuthTokenProvider
 {
     /**
      * An instance of the League OAuth Client Provider.
@@ -120,7 +123,7 @@ class OAuth
      */
     public function getOauth64()
     {
-        // Get a new token if it's not available or has expired
+        //Get a new token if it's not available or has expired
         if (null === $this->oauthToken || $this->oauthToken->hasExpired()) {
             $this->oauthToken = $this->getToken();
         }

lib/phpmailer/OAuthTokenProvider.php

@@ -0,0 +1,44 @@
+<?php
+
+/**
+ * PHPMailer - PHP email creation and transport class.
+ * PHP Version 5.5.
+ *
+ * @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 - 2020 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
+ * @note      This program is distributed in the hope that it will be useful - WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.
+ */
+
+namespace PHPMailer\PHPMailer;
+
+/**
+ * OAuthTokenProvider - OAuth2 token provider interface.
+ * Provides base64 encoded OAuth2 auth strings for SMTP authentication.
+ *
+ * @see     OAuth
+ * @see     SMTP::authenticate()
+ *
+ * @author  Peter Scopes (pdscopes)
+ * @author  Marcus Bointon (Synchro/coolbru) <phpmailer@synchromedia.co.uk>
+ */
+interface OAuthTokenProvider
+{
+    /**
+     * Generate a base64-encoded OAuth token ensuring that the access token has not expired.
+     * The string to be base 64 encoded should be in the form:
+     * "user=<user_email_address>\001auth=Bearer <access_token>\001\001"
+     *
+     * @return string
+     */
+    public function getOauth64();
+}

lib/phpmailer/POP3.php

@@ -1,4 +1,5 @@
 <?php
+
 /**
  * PHPMailer POP-Before-SMTP Authentication Class.
  * PHP Version 5.5.
@@ -9,7 +10,7 @@
  * @author    Jim Jagielski (jimjag) <jimjag@gmail.com>
  * @author    Andy Prevost (codeworxtech) <codeworxtech@users.sourceforge.net>
  * @author    Brent R. Matzelle (original founder)
- * @copyright 2012 - 2019 Marcus Bointon
+ * @copyright 2012 - 2020 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
@@ -18,6 +19,8 @@
  * FITNESS FOR A PARTICULAR PURPOSE.
  */
 
+namespace PHPMailer\PHPMailer;
+
 /**
  * PHPMailer POP-Before-SMTP Authentication Class.
  * Specifically for PHPMailer to use for RFC1939 POP-before-SMTP authentication.
@@ -43,7 +46,7 @@ class POP3
      *
      * @var string
      */
-    const VERSION = '6.1.5';
+    const VERSION = '6.8.0';
 
     /**
      * Default POP3 port number.
@@ -60,12 +63,16 @@ class POP3
     const DEFAULT_TIMEOUT = 30;
 
     /**
-     * Debug display level.
+     * POP3 class debug output mode.
-     * Options: 0 = no, 1+ = yes.
+     * Debug output level.
+     * Options:
+     * @see POP3::DEBUG_OFF: No output
+     * @see POP3::DEBUG_SERVER: Server messages, connection/server errors
+     * @see POP3::DEBUG_CLIENT: Client and Server messages, connection/server errors
      *
      * @var int
      */
-    public $do_debug = 0;
+    public $do_debug = self::DEBUG_OFF;
 
     /**
      * POP3 mail server hostname.
@@ -128,6 +135,28 @@ class POP3
      */
     const LE = "\r\n";
 
+    /**
+     * Debug level for no output.
+     *
+     * @var int
+     */
+    const DEBUG_OFF = 0;
+
+    /**
+     * Debug level to show server -> client messages
+     * also shows clients connection errors or errors from server
+     *
+     * @var int
+     */
+    const DEBUG_SERVER = 1;
+
+    /**
+     * Debug level to show client -> server and server -> client messages.
+     *
+     * @var int
+     */
+    const DEBUG_CLIENT = 2;
+
     /**
      * Simple static wrapper for all-in-one POP before SMTP.
      *
@@ -170,13 +199,13 @@ class POP3
     public function authorise($host, $port = false, $timeout = false, $username = '', $password = '', $debug_level = 0)
     {
         $this->host = $host;
-        // If no port value provided, use default
+        //If no port value provided, use default
         if (false === $port) {
             $this->port = static::DEFAULT_PORT;
         } else {
             $this->port = (int) $port;
         }
-        // If no timeout value provided, use default
+        //If no timeout value provided, use default
         if (false === $timeout) {
             $this->tval = static::DEFAULT_TIMEOUT;
         } else {
@@ -185,9 +214,9 @@ class POP3
         $this->do_debug = $debug_level;
         $this->username = $username;
         $this->password = $password;
-        //  Reset the error log
+        //Reset the error log
         $this->errors = [];
-        //  connect
+        //Connect
         $result = $this->connect($this->host, $this->port, $this->tval);
         if ($result) {
             $login_result = $this->login($this->username, $this->password);
@@ -197,7 +226,7 @@ class POP3
                 return true;
             }
         }
-        // We need to disconnect regardless of whether the login succeeded
+        //We need to disconnect regardless of whether the login succeeded
         $this->disconnect();
 
         return false;
@@ -214,7 +243,7 @@ class POP3
      */
     public function connect($host, $port = false, $tval = 30)
     {
-        //  Are we already connected?
+        //Are we already connected?
         if ($this->connected) {
             return true;
         }
@@ -227,22 +256,22 @@ class POP3
             $port = static::DEFAULT_PORT;
         }
 
-        //  connect to the POP3 server
+        //Connect to the POP3 server
         $errno = 0;
         $errstr = '';
         $this->pop_conn = fsockopen(
-            $host, //  POP3 Host
+            $host, //POP3 Host
-            $port, //  Port #
+            $port, //Port #
-            $errno, //  Error Number
+            $errno, //Error Number
-            $errstr, //  Error Message
+            $errstr, //Error Message
             $tval
-        ); //  Timeout (seconds)
+        ); //Timeout (seconds)
-        //  Restore the error handler
+        //Restore the error handler
         restore_error_handler();
 
-        //  Did we connect?
+        //Did we connect?
         if (false === $this->pop_conn) {
-            //  It would appear not...
+            //It would appear not...
             $this->setError(
                 "Failed to connect to server $host on port $port. errno: $errno; errstr: $errstr"
             );
@@ -250,14 +279,14 @@ class POP3
             return false;
         }
 
-        //  Increase the stream time-out
+        //Increase the stream time-out
         stream_set_timeout($this->pop_conn, $tval, 0);
 
-        //  Get the POP3 server response
+        //Get the POP3 server response
         $pop3_response = $this->getResponse();
-        //  Check for the +OK
+        //Check for the +OK
         if ($this->checkResponse($pop3_response)) {
-            //  The connection is established and the POP3 server is talking
+            //The connection is established and the POP3 server is talking
             $this->connected = true;
 
             return true;
@@ -279,6 +308,7 @@ class POP3
     {
         if (!$this->connected) {
             $this->setError('Not connected to POP3 server');
+            return false;
         }
         if (empty($username)) {
             $username = $this->username;
@@ -287,11 +317,11 @@ class POP3
             $password = $this->password;
         }
 
-        // Send the Username
+        //Send the Username
         $this->sendString("USER $username" . static::LE);
         $pop3_response = $this->getResponse();
         if ($this->checkResponse($pop3_response)) {
-            // Send the Password
+            //Send the Password
             $this->sendString("PASS $password" . static::LE);
             $pop3_response = $this->getResponse();
             if ($this->checkResponse($pop3_response)) {
@@ -307,7 +337,21 @@ class POP3
      */
     public function disconnect()
     {
-        $this->sendString('QUIT');
+        // If could not connect at all, no need to disconnect
+        if ($this->pop_conn === false) {
+            return;
+        }
+
+        $this->sendString('QUIT' . static::LE);
+
+        // RFC 1939 shows POP3 server sending a +OK response to the QUIT command.
+        // Try to get it.  Ignore any failures here.
+        try {
+            $this->getResponse();
+        } catch (Exception $e) {
+            //Do nothing
+        }
+
         //The QUIT command may cause the daemon to exit, which will kill our connection
         //So ignore errors here
         try {
@@ -315,6 +359,10 @@ class POP3
         } catch (Exception $e) {
             //Do nothing
         }
+
+        // Clean up attributes.
+        $this->connected = false;
+        $this->pop_conn  = false;
     }
 
     /**
@@ -327,7 +375,7 @@ class POP3
     protected function getResponse($size = 128)
     {
         $response = fgets($this->pop_conn, $size);
-        if ($this->do_debug >= 1) {
+        if ($this->do_debug >= self::DEBUG_SERVER) {
             echo 'Server -> Client: ', $response;
         }
 
@@ -344,7 +392,7 @@ class POP3
     protected function sendString($string)
     {
         if ($this->pop_conn) {
-            if ($this->do_debug >= 2) { //Show client messages when debug >= 2
+            if ($this->do_debug >= self::DEBUG_CLIENT) { //Show client messages when debug >= 2
                 echo 'Client -> Server: ', $string;
             }
 
@@ -382,7 +430,7 @@ class POP3
     protected function setError($error)
     {
         $this->errors[] = $error;
-        if ($this->do_debug >= 1) {
+        if ($this->do_debug >= self::DEBUG_SERVER) {
             echo '<pre>';
             foreach ($this->errors as $e) {
                 print_r($e);

lib/phpmailer/SMTP.php

@@ -1,4 +1,5 @@
 <?php
+
 /**
  * PHPMailer RFC821 SMTP email transport class.
  * PHP Version 5.5.
@@ -9,7 +10,7 @@
  * @author    Jim Jagielski (jimjag) <jimjag@gmail.com>
  * @author    Andy Prevost (codeworxtech) <codeworxtech@users.sourceforge.net>
  * @author    Brent R. Matzelle (original founder)
- * @copyright 2012 - 2019 Marcus Bointon
+ * @copyright 2012 - 2020 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
@@ -18,6 +19,8 @@
  * FITNESS FOR A PARTICULAR PURPOSE.
  */
 
+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.
@@ -32,7 +35,7 @@ class SMTP
      *
      * @var string
      */
-    const VERSION = '6.1.5';
+    const VERSION = '6.8.0';
 
     /**
      * SMTP line break constant.
@@ -48,6 +51,13 @@ class SMTP
      */
     const DEFAULT_PORT = 25;
 
+    /**
+     * The SMTPs port to use if one is not specified.
+     *
+     * @var int
+     */
+    const DEFAULT_SECURE_PORT = 465;
+
     /**
      * The maximum line length allowed by RFC 5321 section 4.5.3.1.6,
      * *excluding* a trailing CRLF break.
@@ -183,6 +193,9 @@ class SMTP
         'Amazon_SES' => '/[\d]{3} Ok (.*)/',
         'SendGrid' => '/[\d]{3} Ok: queued as (.*)/',
         'CampaignMonitor' => '/[\d]{3} 2.0.0 OK:([a-zA-Z\d]{48})/',
+        'Haraka' => '/[\d]{3} Message Queued \((.*)\)/',
+        'ZoneMTA' => '/[\d]{3} Message queued as (.*)/',
+        'Mailjet' => '/[\d]{3} OK queued as (.*)/',
     ];
 
     /**
@@ -309,17 +322,11 @@ class SMTP
      */
     public function connect($host, $port = null, $timeout = 30, $options = [])
     {
-        static $streamok;
+        //Clear errors to avoid confusion
-        //This is enabled by default since 5.0.0 but some providers disable it
-        //Check this once and cache the result
-        if (null === $streamok) {
-            $streamok = function_exists('stream_socket_client');
-        }
-        // Clear errors to avoid confusion
         $this->setError('');
-        // Make sure we are __not__ connected
+        //Make sure we are __not__ connected
         if ($this->connected()) {
-            // Already connected, generate error
+            //Already connected, generate error
             $this->setError('Already connected to a server');
 
             return false;
@@ -327,18 +334,66 @@ class SMTP
         if (empty($port)) {
             $port = self::DEFAULT_PORT;
         }
-        // Connect to the SMTP server
+        //Connect to the SMTP server
         $this->edebug(
             "Connection: opening to $host:$port, timeout=$timeout, options=" .
             (count($options) > 0 ? var_export($options, true) : 'array()'),
             self::DEBUG_CONNECTION
         );
+
+        $this->smtp_conn = $this->getSMTPConnection($host, $port, $timeout, $options);
+
+        if ($this->smtp_conn === false) {
+            //Error info already set inside `getSMTPConnection()`
+            return false;
+        }
+
+        $this->edebug('Connection: opened', self::DEBUG_CONNECTION);
+
+        //Get any announcement
+        $this->last_reply = $this->get_lines();
+        $this->edebug('SERVER -> CLIENT: ' . $this->last_reply, self::DEBUG_SERVER);
+        $responseCode = (int)substr($this->last_reply, 0, 3);
+        if ($responseCode === 220) {
+            return true;
+        }
+        //Anything other than a 220 response means something went wrong
+        //RFC 5321 says the server will wait for us to send a QUIT in response to a 554 error
+        //https://tools.ietf.org/html/rfc5321#section-3.1
+        if ($responseCode === 554) {
+            $this->quit();
+        }
+        //This will handle 421 responses which may not wait for a QUIT (e.g. if the server is being shut down)
+        $this->edebug('Connection: closing due to error', self::DEBUG_CONNECTION);
+        $this->close();
+        return false;
+    }
+
+    /**
+     * Create connection to the SMTP server.
+     *
+     * @param string $host    SMTP server IP or host name
+     * @param int    $port    The port number to connect to
+     * @param int    $timeout How long to wait for the connection to open
+     * @param array  $options An array of options for stream_context_create()
+     *
+     * @return false|resource
+     */
+    protected function getSMTPConnection($host, $port = null, $timeout = 30, $options = [])
+    {
+        static $streamok;
+        //This is enabled by default since 5.0.0 but some providers disable it
+        //Check this once and cache the result
+        if (null === $streamok) {
+            $streamok = function_exists('stream_socket_client');
+        }
+
         $errno = 0;
         $errstr = '';
         if ($streamok) {
             $socket_context = stream_context_create($options);
             set_error_handler([$this, 'errorHandler']);
-            $this->smtp_conn = stream_socket_client(
+            $connection = stream_socket_client(
                 $host . ':' . $port,
                 $errno,
                 $errstr,
@@ -346,7 +401,6 @@ class SMTP
                 STREAM_CLIENT_CONNECT,
                 $socket_context
             );
-            restore_error_handler();
         } else {
             //Fall back to fsockopen which should work in more places, but is missing some features
             $this->edebug(
@@ -354,17 +408,18 @@ class SMTP
                 self::DEBUG_CONNECTION
             );
             set_error_handler([$this, 'errorHandler']);
-            $this->smtp_conn = fsockopen(
+            $connection = fsockopen(
                 $host,
                 $port,
                 $errno,
                 $errstr,
                 $timeout
             );
-            restore_error_handler();
         }
-        // Verify we connected properly
+        restore_error_handler();
-        if (!is_resource($this->smtp_conn)) {
+
+        //Verify we connected properly
+        if (!is_resource($connection)) {
             $this->setError(
                 'Failed to connect to server',
                 '',
@@ -379,22 +434,19 @@ class SMTP
 
             return false;
         }
-        $this->edebug('Connection: opened', self::DEBUG_CONNECTION);
+
-        // SMTP server can take longer to respond, give longer timeout for first read
+        //SMTP server can take longer to respond, give longer timeout for first read
-        // Windows does not have support for this timeout function
+        //Windows does not have support for this timeout function
         if (strpos(PHP_OS, 'WIN') !== 0) {
-            $max = (int) ini_get('max_execution_time');
+            $max = (int)ini_get('max_execution_time');
-            // Don't bother if unlimited
+            //Don't bother if unlimited, or if set_time_limit is disabled
-            if (0 !== $max && $timeout > $max) {
+            if (0 !== $max && $timeout > $max && strpos(ini_get('disable_functions'), 'set_time_limit') === false) {
                 @set_time_limit($timeout);
             }
-            stream_set_timeout($this->smtp_conn, $timeout, 0);
+            stream_set_timeout($connection, $timeout, 0);
         }
-        // Get any announcement
-        $announce = $this->get_lines();
-        $this->edebug('SERVER -> CLIENT: ' . $announce, self::DEBUG_SERVER);
 
-        return true;
+        return $connection;
     }
 
     /**
@@ -418,7 +470,7 @@ class SMTP
             $crypto_method |= STREAM_CRYPTO_METHOD_TLSv1_1_CLIENT;
         }
 
-        // Begin encrypted connection
+        //Begin encrypted connection
         set_error_handler([$this, 'errorHandler']);
         $crypto_ok = stream_socket_enable_crypto(
             $this->smtp_conn,
@@ -439,7 +491,7 @@ class SMTP
      * @param string $username The user name
      * @param string $password The password
      * @param string $authtype The auth type (CRAM-MD5, PLAIN, LOGIN, XOAUTH2)
-     * @param OAuth  $OAuth    An optional OAuth instance for XOAUTH2 authentication
+     * @param OAuthTokenProvider $OAuth An optional OAuthTokenProvider instance for XOAUTH2 authentication
      *
      * @return bool True if successfully authenticated
      */
@@ -456,11 +508,11 @@ class SMTP
         }
 
         if (array_key_exists('EHLO', $this->server_caps)) {
-            // SMTP extensions are available; try to find a proper authentication method
+            //SMTP extensions are available; try to find a proper authentication method
             if (!array_key_exists('AUTH', $this->server_caps)) {
                 $this->setError('Authentication is not allowed at this stage');
-                // 'at this stage' means that auth may be allowed after the stage changes
+                //'at this stage' means that auth may be allowed after the stage changes
-                // e.g. after STARTTLS
+                //e.g. after STARTTLS
 
                 return false;
             }
@@ -504,22 +556,25 @@ class SMTP
         }
         switch ($authtype) {
             case 'PLAIN':
-                // Start authentication
+                //Start authentication
                 if (!$this->sendCommand('AUTH', 'AUTH PLAIN', 334)) {
                     return false;
                 }
-                // Send encoded username and password
+                //Send encoded username and password
-                if (!$this->sendCommand(
+                if (
-                    'User & Password',
+                    //Format from https://tools.ietf.org/html/rfc4616#section-2
-                    base64_encode("\0" . $username . "\0" . $password),
+                    //We skip the first field (it's forgery), so the string starts with a null byte
-                    235
+                    !$this->sendCommand(
-                )
+                        'User & Password',
+                        base64_encode("\0" . $username . "\0" . $password),
+                        235
+                    )
                 ) {
                     return false;
                 }
                 break;
             case 'LOGIN':
-                // Start authentication
+                //Start authentication
                 if (!$this->sendCommand('AUTH', 'AUTH LOGIN', 334)) {
                     return false;
                 }
@@ -531,17 +586,17 @@ class SMTP
                 }
                 break;
             case 'CRAM-MD5':
-                // Start authentication
+                //Start authentication
                 if (!$this->sendCommand('AUTH CRAM-MD5', 'AUTH CRAM-MD5', 334)) {
                     return false;
                 }
-                // Get the challenge
+                //Get the challenge
                 $challenge = base64_decode(substr($this->last_reply, 4));
 
-                // Build the response
+                //Build the response
                 $response = $username . ' ' . $this->hmac($challenge, $password);
 
-                // send encoded credentials
+                //send encoded credentials
                 return $this->sendCommand('Username', base64_encode($response), 235);
             case 'XOAUTH2':
                 //The OAuth instance must be set up prior to requesting auth.
@@ -550,7 +605,7 @@ class SMTP
                 }
                 $oauth = $OAuth->getOauth64();
 
-                // Start authentication
+                //Start authentication
                 if (!$this->sendCommand('AUTH', 'AUTH XOAUTH2 ' . $oauth, 235)) {
                     return false;
                 }
@@ -580,15 +635,15 @@ class SMTP
             return hash_hmac('md5', $data, $key);
         }
 
-        // The following borrowed from
+        //The following borrowed from
-        // http://php.net/manual/en/function.mhash.php#27225
+        //http://php.net/manual/en/function.mhash.php#27225
 
-        // RFC 2104 HMAC implementation for php.
+        //RFC 2104 HMAC implementation for php.
-        // Creates an md5 HMAC.
+        //Creates an md5 HMAC.
-        // Eliminates the need to install mhash to compute a HMAC
+        //Eliminates the need to install mhash to compute a HMAC
-        // by Lance Rushing
+        //by Lance Rushing
 
-        $bytelen = 64; // byte length for md5
+        $bytelen = 64; //byte length for md5
         if (strlen($key) > $bytelen) {
             $key = pack('H*', md5($key));
         }
@@ -611,7 +666,7 @@ class SMTP
         if (is_resource($this->smtp_conn)) {
             $sock_status = stream_get_meta_data($this->smtp_conn);
             if ($sock_status['eof']) {
-                // The socket is valid but we are not connected
+                //The socket is valid but we are not connected
                 $this->edebug(
                     'SMTP NOTICE: EOF caught while checking if connected',
                     self::DEBUG_CLIENT
@@ -621,7 +676,7 @@ class SMTP
                 return false;
             }
 
-            return true; // everything looks good
+            return true; //everything looks good
         }
 
         return false;
@@ -635,11 +690,10 @@ class SMTP
      */
     public function close()
     {
-        $this->setError('');
         $this->server_caps = null;
         $this->helo_rply = null;
         if (is_resource($this->smtp_conn)) {
-            // close the connection and cleanup
+            //Close the connection and cleanup
             fclose($this->smtp_conn);
             $this->smtp_conn = null; //Makes for cleaner serialization
             $this->edebug('Connection: closed', self::DEBUG_CONNECTION);
@@ -649,7 +703,7 @@ class SMTP
     /**
      * Send an SMTP DATA command.
      * Issues a data command and sends the msg_data to the server,
-     * finializing the mail transaction. $msg_data is the message
+     * finalizing the mail transaction. $msg_data is the message
      * that is to be send with the headers. Each header needs to be
      * on a single line followed by a <CRLF> with the message headers
      * and the message body being separated by an additional <CRLF>.
@@ -674,7 +728,7 @@ class SMTP
          * NOTE: this does not count towards line-length limit.
          */
 
-        // Normalize line breaks before exploding
+        //Normalize line breaks before exploding
         $lines = explode("\n", str_replace(["\r\n", "\r"], "\n", $msg_data));
 
         /* To distinguish between a complete RFC822 message and a plain message body, we check if the first field
@@ -720,7 +774,8 @@ class SMTP
 
             //Send the lines to the server
             foreach ($lines_out as $line_out) {
-                //RFC2821 section 4.5.2
+                //Dot-stuffing as per RFC5321 section 4.5.2
+                //https://tools.ietf.org/html/rfc5321#section-4.5.2
                 if (!empty($line_out) && $line_out[0] === '.') {
                     $line_out = '.' . $line_out;
                 }
@@ -754,7 +809,16 @@ class SMTP
     public function hello($host = '')
     {
         //Try extended hello first (RFC 2821)
-        return $this->sendHello('EHLO', $host) or $this->sendHello('HELO', $host);
+        if ($this->sendHello('EHLO', $host)) {
+            return true;
+        }
+
+        //Some servers shut down the SMTP service here (RFC 5321)
+        if (substr($this->helo_rply, 0, 3) == '421') {
+            return false;
+        }
+
+        return $this->sendHello('HELO', $host);
     }
 
     /**
@@ -944,12 +1008,12 @@ class SMTP
         $this->client_send($commandstring . static::LE, $command);
 
         $this->last_reply = $this->get_lines();
-        // Fetch SMTP code and possible error code explanation
+        //Fetch SMTP code and possible error code explanation
         $matches = [];
         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
+            //Cut off error code from each response line
             $detail = preg_replace(
                 "/{$code}[ -]" .
                 ($code_ex ? str_replace('.', '\\.', $code_ex) . ' ' : '') . '/m',
@@ -957,7 +1021,7 @@ class SMTP
                 $this->last_reply
             );
         } else {
-            // Fall back to simple parsing if regex fails
+            //Fall back to simple parsing if regex fails
             $code = (int) substr($this->last_reply, 0, 3);
             $code_ex = null;
             $detail = substr($this->last_reply, 4);
@@ -980,7 +1044,10 @@ class SMTP
             return false;
         }
 
-        $this->setError('');
+        //Don't clear the error store when using keepalive
+        if ($command !== 'RSET') {
+            $this->setError('');
+        }
 
         return true;
     }
@@ -1056,8 +1123,10 @@ 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 > $this->do_debug &&
+        if (
-            in_array($command, ['User & Password', 'Username', 'Password'], true)) {
+            self::DEBUG_LOWLEVEL > $this->do_debug &&
+            in_array($command, ['User & Password', 'Username', 'Password'], true)
+        ) {
             $this->edebug('CLIENT -> SERVER: [credentials hidden]', self::DEBUG_CLIENT);
         } else {
             $this->edebug('CLIENT -> SERVER: ' . $data, self::DEBUG_CLIENT);
@@ -1111,7 +1180,7 @@ class SMTP
         if (!$this->server_caps) {
             $this->setError('No HELO/EHLO was sent');
 
-            return;
+            return null;
         }
 
         if (!array_key_exists($name, $this->server_caps)) {
@@ -1123,7 +1192,7 @@ class SMTP
             }
             $this->setError('HELO handshake was used; No information about server extensions available');
 
-            return;
+            return null;
         }
 
         return $this->server_caps[$name];
@@ -1150,7 +1219,7 @@ class SMTP
      */
     protected function get_lines()
     {
-        // If the connection is bad, give up straight away
+        //If the connection is bad, give up straight away
         if (!is_resource($this->smtp_conn)) {
             return '';
         }
@@ -1164,33 +1233,61 @@ class SMTP
         $selW = null;
         while (is_resource($this->smtp_conn) && !feof($this->smtp_conn)) {
             //Must pass vars in here as params are by reference
-            if (!stream_select($selR, $selW, $selW, $this->Timelimit)) {
+            //solution for signals inspired by https://github.com/symfony/symfony/pull/6540
+            set_error_handler([$this, 'errorHandler']);
+            $n = stream_select($selR, $selW, $selW, $this->Timelimit);
+            restore_error_handler();
+
+            if ($n === false) {
+                $message = $this->getError()['detail'];
+
                 $this->edebug(
-                    'SMTP -> get_lines(): timed-out (' . $this->Timeout . ' sec)',
+                    'SMTP -> get_lines(): select failed (' . $message . ')',
+                    self::DEBUG_LOWLEVEL
+                );
+
+                //stream_select returns false when the `select` system call is interrupted
+                //by an incoming signal, try the select again
+                if (stripos($message, 'interrupted system call') !== false) {
+                    $this->edebug(
+                        'SMTP -> get_lines(): retrying stream_select',
+                        self::DEBUG_LOWLEVEL
+                    );
+                    $this->setError('');
+                    continue;
+                }
+
+                break;
+            }
+
+            if (!$n) {
+                $this->edebug(
+                    'SMTP -> get_lines(): select timed-out in (' . $this->Timelimit . ' sec)',
                     self::DEBUG_LOWLEVEL
                 );
                 break;
             }
+
             //Deliberate noise suppression - errors are handled afterwards
             $str = @fgets($this->smtp_conn, self::MAX_REPLY_LENGTH);
             $this->edebug('SMTP INBOUND: "' . trim($str) . '"', self::DEBUG_LOWLEVEL);
             $data .= $str;
-            // If response is only 3 chars (not valid, but RFC5321 S4.2 says it must be handled),
+            //If response is only 3 chars (not valid, but RFC5321 S4.2 says it must be handled),
-            // or 4th character is a space or a line break char, we are done reading, break the loop.
+            //or 4th character is a space or a line break char, we are done reading, break the loop.
-            // String array access is a significant micro-optimisation over strlen
+            //String array access is a significant micro-optimisation over strlen
             if (!isset($str[3]) || $str[3] === ' ' || $str[3] === "\r" || $str[3] === "\n") {
                 break;
             }
-            // Timed-out? Log and break
+            //Timed-out? Log and break
             $info = stream_get_meta_data($this->smtp_conn);
             if ($info['timed_out']) {
                 $this->edebug(
-                    'SMTP -> get_lines(): timed-out (' . $this->Timeout . ' sec)',
+                    'SMTP -> get_lines(): stream timed-out (' . $this->Timeout . ' sec)',
                     self::DEBUG_LOWLEVEL
                 );
                 break;
             }
-            // Now check if reads took too long
+            //Now check if reads took too long
             if ($endtime && time() > $endtime) {
                 $this->edebug(
                     'SMTP -> get_lines(): timelimit reached (' .