diff --git a/wp-includes/class-phpmailer.php b/wp-includes/class-phpmailer.php
index 338965ff4b..f83697d92b 100644
--- a/wp-includes/class-phpmailer.php
+++ b/wp-includes/class-phpmailer.php
@@ -29,65 +29,66 @@ class PHPMailer
 {
     /**
      * The PHPMailer Version number.
-     * @type string
+     * @var string
      */
-    public $Version = '5.2.10';
+    public $Version = '5.2.21';
 
     /**
      * Email priority.
-     * Options: 1 = High, 3 = Normal, 5 = low.
-     * @type integer
+     * Options: null (default), 1 = High, 3 = Normal, 5 = low.
+     * When null, the header is not set at all.
+     * @var integer
      */
-    public $Priority = 3;
+    public $Priority = null;
 
     /**
      * The character set of the message.
-     * @type string
+     * @var string
      */
     public $CharSet = 'iso-8859-1';
 
     /**
      * The MIME Content-type of the message.
-     * @type string
+     * @var string
      */
     public $ContentType = 'text/plain';
 
     /**
      * The message encoding.
      * Options: "8bit", "7bit", "binary", "base64", and "quoted-printable".
-     * @type string
+     * @var string
      */
     public $Encoding = '8bit';
 
     /**
      * Holds the most recent mailer error message.
-     * @type string
+     * @var string
      */
     public $ErrorInfo = '';
 
     /**
      * The From email address for the message.
-     * @type string
+     * @var string
      */
     public $From = 'root@localhost';
 
     /**
      * The From name of the message.
-     * @type string
+     * @var string
      */
     public $FromName = 'Root User';
 
     /**
      * The Sender email (Return-Path) of the message.
      * If not empty, will be sent via -f to sendmail or as 'MAIL FROM' in smtp mode.
-     * @type string
+     * @var string
      */
     public $Sender = '';
 
     /**
      * The Return-Path of the message.
      * If empty, it will be set to either From or Sender.
-     * @type string
+     * @var string
      * @deprecated Email senders should never set a return-path header;
      * it's the receiver's job (RFC5321 section 4.4), so this no longer does anything.
      * @link https://tools.ietf.org/html/rfc5321#section-4.4 RFC5321 reference
@@ -96,14 +97,14 @@ class PHPMailer
 
     /**
      * The Subject of the message.
-     * @type string
+     * @var string
      */
     public $Subject = '';
 
     /**
      * An HTML or plain text message body.
      * If HTML then call isHTML(true).
-     * @type string
+     * @var string
      */
     public $Body = '';
 
@@ -112,7 +113,7 @@ class PHPMailer
      * This body can be read by mail clients that do not have HTML email
      * capability such as mutt & Eudora.
      * Clients that can read HTML will view the normal Body.
-     * @type string
+     * @var string
      */
     public $AltBody = '';
 
@@ -122,27 +123,27 @@ class PHPMailer
      * To generate iCal events, use the bundled extras/EasyPeasyICS.php class or iCalcreator
      * @link http://sprain.ch/blog/downloads/php-class-easypeasyics-create-ical-files-with-php/
      * @link http://kigkonsult.se/iCalcreator/
-     * @type string
+     * @var string
      */
     public $Ical = '';
 
     /**
      * The complete compiled MIME message body.
      * @access protected
-     * @type string
+     * @var string
      */
     protected $MIMEBody = '';
 
     /**
      * The complete compiled MIME message headers.
-     * @type string
+     * @var string
      * @access protected
      */
     protected $MIMEHeader = '';
 
     /**
      * Extra headers that createHeader() doesn't fold in.
-     * @type string
+     * @var string
      * @access protected
      */
     protected $mailHeader = '';
@@ -150,64 +151,67 @@ class PHPMailer
     /**
      * Word-wrap the message body to this number of chars.
      * Set to 0 to not wrap. A useful value here is 78, for RFC2822 section 2.1.1 compliance.
-     * @type integer
+     * @var integer
      */
     public $WordWrap = 0;
 
     /**
      * Which method to use to send mail.
      * Options: "mail", "sendmail", or "smtp".
-     * @type string
+     * @var string
      */
     public $Mailer = 'mail';
 
     /**
      * The path to the sendmail program.
-     * @type string
+     * @var string
      */
     public $Sendmail = '/usr/sbin/sendmail';
 
     /**
      * Whether mail() uses a fully sendmail-compatible MTA.
      * One which supports sendmail's "-oi -f" options.
-     * @type boolean
+     * @var boolean
      */
     public $UseSendmailOptions = true;
 
     /**
      * Path to PHPMailer plugins.
      * Useful if the SMTP class is not in the PHP include path.
-     * @type string
+     * @var string
      * @deprecated Should not be needed now there is an autoloader.
      */
     public $PluginDir = '';
 
     /**
-     * The email address that a reading confirmation should be sent to.
-     * @type string
+     * The email address that a reading confirmation should be sent to, also known as read receipt.
+     * @var string
      */
     public $ConfirmReadingTo = '';
 
     /**
-     * The hostname to use in Message-Id and Received headers
-     * and as default HELO string.
-     * If empty, the value returned
-     * by SERVER_NAME is used or 'localhost.localdomain'.
-     * @type string
+     * The hostname to use in the Message-ID header and as default HELO string.
+     * If empty, PHPMailer attempts to find one with, in order,
+     * $_SERVER['SERVER_NAME'], gethostname(), php_uname('n'), or the value
+     * 'localhost.localdomain'.
+     * @var string
      */
     public $Hostname = '';
 
     /**
-     * An ID to be used in the Message-Id header.
+     * An ID to be used in the Message-ID header.
      * If empty, a unique id will be generated.
-     * @type string
+     * You can set your own, but it must be in the format "<id@domain>",
+     * as defined in RFC5322 section 3.6.4 or it will be ignored.
+     * @see https://tools.ietf.org/html/rfc5322#section-3.6.4
+     * @var string
      */
     public $MessageID = '';
 
     /**
      * The message Date to be used in the Date header.
      * If empty, the current date will be added.
-     * @type string
+     * @var string
      */
     public $MessageDate = '';
 
@@ -220,21 +224,22 @@ class PHPMailer
      * You can also specify encryption type, for example:
      * (e.g. "tls://smtp1.example.com:587;ssl://smtp2.example.com:465").
      * Hosts will be tried in order.
-     * @type string
+     * @var string
      */
     public $Host = 'localhost';
 
     /**
      * The default SMTP server port.
-     * @type integer
+     * @var integer
      * @TODO Why is this needed when the SMTP class takes care of it?
      */
     public $Port = 25;
 
     /**
      * The SMTP HELO of the message.
-     * Default is $Hostname.
-     * @type string
+     * Default is $Hostname. If $Hostname is empty, PHPMailer attempts to find
+     * one with the same method described above for $Hostname.
+     * @var string
      * @see PHPMailer::$Hostname
      */
     public $Helo = '';
@@ -242,7 +247,7 @@ class PHPMailer
     /**
      * What kind of encryption to use on the SMTP connection.
      * Options: '', 'ssl' or 'tls'
-     * @type string
+     * @var string
      */
     public $SMTPSecure = '';
 
@@ -250,14 +255,14 @@ class PHPMailer
      * Whether to enable TLS encryption automatically if a server supports it,
      * even if `SMTPSecure` is not set to 'tls'.
      * Be aware that in PHP >= 5.6 this requires that the server's certificates are valid.
-     * @type boolean
+     * @var boolean
      */
     public $SMTPAutoTLS = true;
 
     /**
      * Whether to use SMTP authentication.
      * Uses the Username and Password properties.
-     * @type boolean
+     * @var boolean
      * @see PHPMailer::$Username
      * @see PHPMailer::$Password
      */
@@ -265,47 +270,47 @@ class PHPMailer
 
     /**
      * Options array passed to stream_context_create when connecting via SMTP.
-     * @type array
+     * @var array
      */
     public $SMTPOptions = array();
 
     /**
      * SMTP username.
-     * @type string
+     * @var string
      */
     public $Username = '';
 
     /**
      * SMTP password.
-     * @type string
+     * @var string
      */
     public $Password = '';
 
     /**
      * SMTP auth type.
-     * Options are LOGIN (default), PLAIN, NTLM, CRAM-MD5
-     * @type string
+     * Options are CRAM-MD5, LOGIN, PLAIN, attempted in that order if not specified
+     * @var string
      */
     public $AuthType = '';
 
     /**
      * SMTP realm.
      * Used for NTLM auth
-     * @type string
+     * @var string
      */
     public $Realm = '';
 
     /**
      * SMTP workstation.
      * Used for NTLM auth
-     * @type string
+     * @var string
      */
     public $Workstation = '';
 
     /**
      * The SMTP server timeout in seconds.
      * Default of 5 minutes (300sec) is from RFC2821 section 4.5.3.2
-     * @type integer
+     * @var integer
      */
     public $Timeout = 300;
 
@@ -318,7 +323,7 @@ class PHPMailer
      * * `2` Data and commands
      * * `3` As 2 plus connection status
      * * `4` Low-level data output
-     * @type integer
+     * @var integer
      * @see SMTP::$do_debug
      */
     public $SMTPDebug = 0;
@@ -334,7 +339,7 @@ class PHPMailer
      * <code>
      * $mail->Debugoutput = function($str, $level) {echo "debug level $level; message: $str";};
      * </code>
-     * @type string|callable
+     * @var string|callable
      * @see SMTP::$Debugoutput
      */
     public $Debugoutput = 'echo';
@@ -343,20 +348,21 @@ class PHPMailer
      * Whether to keep SMTP connection open after each message.
      * If this is set to true then to close the connection
      * requires an explicit call to smtpClose().
-     * @type boolean
+     * @var boolean
      */
     public $SMTPKeepAlive = false;
 
     /**
      * Whether to split multiple to addresses into multiple messages
      * or send them all in one message.
-     * @type boolean
+     * Only supported in `mail` and `sendmail` transports, not in SMTP.
+     * @var boolean
      */
     public $SingleTo = false;
 
     /**
      * Storage for addresses when SingleTo is enabled.
-     * @type array
+     * @var array
      * @TODO This should really not be public
      */
     public $SingleToArray = array();
@@ -364,15 +370,15 @@ class PHPMailer
     /**
      * Whether to generate VERP addresses on send.
      * Only applicable when sending via SMTP.
-     * @link http://en.wikipedia.org/wiki/Variable_envelope_return_path
+     * @link https://en.wikipedia.org/wiki/Variable_envelope_return_path
      * @link http://www.postfix.org/VERP_README.html Postfix VERP info
-     * @type boolean
+     * @var boolean
      */
     public $do_verp = false;
 
     /**
      * Whether to allow sending messages with an empty body.
-     * @type boolean
+     * @var boolean
      */
     public $AllowEmpty = false;
 
@@ -380,43 +386,50 @@ class PHPMailer
      * The default line ending.
      * @note The default remains "\n". We force CRLF where we know
      *        it must be used via self::CRLF.
-     * @type string
+     * @var string
      */
     public $LE = "\n";
 
     /**
      * DKIM selector.
-     * @type string
+     * @var string
      */
     public $DKIM_selector = '';
 
     /**
      * DKIM Identity.
-     * Usually the email address used as the source of the email
-     * @type string
+     * Usually the email address used as the source of the email.
+     * @var string
      */
     public $DKIM_identity = '';
 
     /**
      * DKIM passphrase.
      * Used if your key is encrypted.
-     * @type string
+     * @var string
      */
     public $DKIM_passphrase = '';
 
     /**
      * DKIM signing domain name.
      * @example 'example.com'
-     * @type string
+     * @var string
      */
     public $DKIM_domain = '';
 
     /**
      * DKIM private key file path.
-     * @type string
+     * @var string
      */
     public $DKIM_private = '';
 
+    /**
+     * DKIM private key string.
+     * If set, takes precedence over `$DKIM_private`.
+     * @var string
+     */
+    public $DKIM_private_string = '';
+
     /**
      * Callback Action function name.
      *
@@ -433,48 +446,57 @@ class PHPMailer
      *   string  $subject       the subject
      *   string  $body          the email body
      *   string  $from          email address of sender
-     * @type string
+     * @var string
      */
     public $action_function = '';
 
     /**
      * What to put in the X-Mailer header.
      * Options: An empty string for PHPMailer default, whitespace for none, or a string to use
-     * @type string
+     * @var string
      */
     public $XMailer = '';
 
+    /**
+     * Which validator to use by default when validating email addresses.
+     * May be a callable to inject your own validator, but there are several built-in validators.
+     * @see PHPMailer::validateAddress()
+     * @var string|callable
+     * @static
+     */
+    public static $validator = 'auto';
+
     /**
      * An instance of the SMTP sender class.
-     * @type SMTP
+     * @var SMTP
      * @access protected
      */
     protected $smtp = null;
 
     /**
-     * The array of 'to' addresses.
-     * @type array
+     * The array of 'to' names and addresses.
+     * @var array
      * @access protected
      */
     protected $to = array();
 
     /**
-     * The array of 'cc' addresses.
-     * @type array
+     * The array of 'cc' names and addresses.
+     * @var array
      * @access protected
      */
     protected $cc = array();
 
     /**
-     * The array of 'bcc' addresses.
-     * @type array
+     * The array of 'bcc' names and addresses.
+     * @var array
      * @access protected
      */
     protected $bcc = array();
 
     /**
      * The array of reply-to names and addresses.
-     * @type array
+     * @var array
      * @access protected
      */
     protected $ReplyTo = array();
@@ -482,77 +504,100 @@ class PHPMailer
     /**
      * An array of all kinds of addresses.
      * Includes all of $to, $cc, $bcc
-     * @type array
+     * @var array
      * @access protected
+     * @see PHPMailer::$to @see PHPMailer::$cc @see PHPMailer::$bcc
      */
     protected $all_recipients = array();
 
+    /**
+     * An array of names and addresses queued for validation.
+     * In send(), valid and non duplicate entries are moved to $all_recipients
+     * and one of $to, $cc, or $bcc.
+     * This array is used only for addresses with IDN.
+     * @var array
+     * @access protected
+     * @see PHPMailer::$to @see PHPMailer::$cc @see PHPMailer::$bcc
+     * @see PHPMailer::$all_recipients
+     */
+    protected $RecipientsQueue = array();
+
+    /**
+     * An array of reply-to names and addresses queued for validation.
+     * In send(), valid and non duplicate entries are moved to $ReplyTo.
+     * This array is used only for addresses with IDN.
+     * @var array
+     * @access protected
+     * @see PHPMailer::$ReplyTo
+     */
+    protected $ReplyToQueue = array();
+
     /**
      * The array of attachments.
-     * @type array
+     * @var array
      * @access protected
      */
     protected $attachment = array();
 
     /**
      * The array of custom headers.
-     * @type array
+     * @var array
      * @access protected
      */
     protected $CustomHeader = array();
 
     /**
      * The most recent Message-ID (including angular brackets).
-     * @type string
+     * @var string
      * @access protected
      */
     protected $lastMessageID = '';
 
     /**
      * The message's MIME type.
-     * @type string
+     * @var string
      * @access protected
      */
     protected $message_type = '';
 
     /**
      * The array of MIME boundary strings.
-     * @type array
+     * @var array
      * @access protected
      */
     protected $boundary = array();
 
     /**
      * The array of available languages.
-     * @type array
+     * @var array
      * @access protected
      */
     protected $language = array();
 
     /**
      * The number of errors encountered.
-     * @type integer
+     * @var integer
      * @access protected
      */
     protected $error_count = 0;
 
     /**
      * The S/MIME certificate file path.
-     * @type string
+     * @var string
      * @access protected
      */
     protected $sign_cert_file = '';
 
     /**
      * The S/MIME key file path.
-     * @type string
+     * @var string
      * @access protected
      */
     protected $sign_key_file = '';
 
     /**
      * The optional S/MIME extra certificates ("CA Chain") file path.
-     * @type string
+     * @var string
      * @access protected
      */
     protected $sign_extracerts_file = '';
@@ -560,21 +605,21 @@ class PHPMailer
     /**
      * The S/MIME password for the key.
      * Used only if the key is encrypted.
-     * @type string
+     * @var string
      * @access protected
      */
     protected $sign_key_pass = '';
 
     /**
      * Whether to throw exceptions for errors.
-     * @type boolean
+     * @var boolean
      * @access protected
      */
     protected $exceptions = false;
 
     /**
      * Unique ID used for message ID and boundaries.
-     * @type string
+     * @var string
      * @access protected
      */
     protected $uniqueid = '';
@@ -601,7 +646,7 @@ class PHPMailer
 
     /**
      * The maximum line length allowed by RFC 2822 section 2.1.1
-     * @type integer
+     * @var integer
      */
     const MAX_LINE_LENGTH = 998;
 
@@ -609,9 +654,11 @@ class PHPMailer
      * Constructor.
      * @param boolean $exceptions Should we throw external exceptions?
      */
-    public function __construct($exceptions = false)
+    public function __construct($exceptions = null)
     {
-        $this->exceptions = (boolean)$exceptions;
+        if ($exceptions !== null) {
+            $this->exceptions = (boolean)$exceptions;
+        }
     }
 
     /**
@@ -620,9 +667,7 @@ class PHPMailer
     public function __destruct()
     {
         //Close any open SMTP connection nicely
-        if ($this->Mailer == 'smtp') {
-            $this->smtpClose();
-        }
+        $this->smtpClose();
     }
 
     /**
@@ -646,14 +691,16 @@ class PHPMailer
         } else {
             $subject = $this->encodeHeader($this->secureHeader($subject));
         }
-        if (ini_get('safe_mode') || !($this->UseSendmailOptions)) {
+
+        //Can't use additional_parameters in safe_mode, calling mail() with null params breaks
+        //@link http://php.net/manual/en/function.mail.php
+        if (ini_get('safe_mode') or !$this->UseSendmailOptions or is_null($params)) {
             $result = @mail($to, $subject, $body, $header);
         } else {
             $result = @mail($to, $subject, $body, $header, $params);
         }
         return $result;
     }
-
     /**
      * Output debugging info via user-defined method.
      * Only generates output if SMTP debug output is enabled (@see SMTP::$do_debug).
@@ -688,7 +735,7 @@ class PHPMailer
             case 'echo':
             default:
                 //Normalize line breaks
-                $str = preg_replace('/(\r\n|\r|\n)/ms', "\n", $str);
+                $str = preg_replace('/\r\n?/ms', "\n", $str);
                 echo gmdate('Y-m-d H:i:s') . "\t" . str_replace(
                     "\n",
                     "\n                   \t                  ",
@@ -763,55 +810,101 @@ class PHPMailer
 
     /**
      * Add a "To" address.
-     * @param string $address
+     * @param string $address The email address to send to
      * @param string $name
-     * @return boolean true on success, false if address already used
+     * @return boolean true on success, false if address already used or invalid in some way
      */
     public function addAddress($address, $name = '')
     {
-        return $this->addAnAddress('to', $address, $name);
+        return $this->addOrEnqueueAnAddress('to', $address, $name);
     }
 
     /**
      * Add a "CC" address.
      * @note: This function works with the SMTP mailer on win32, not with the "mail" mailer.
-     * @param string $address
+     * @param string $address The email address to send to
      * @param string $name
-     * @return boolean true on success, false if address already used
+     * @return boolean true on success, false if address already used or invalid in some way
      */
     public function addCC($address, $name = '')
     {
-        return $this->addAnAddress('cc', $address, $name);
+        return $this->addOrEnqueueAnAddress('cc', $address, $name);
     }
 
     /**
      * Add a "BCC" address.
      * @note: This function works with the SMTP mailer on win32, not with the "mail" mailer.
-     * @param string $address
+     * @param string $address The email address to send to
      * @param string $name
-     * @return boolean true on success, false if address already used
+     * @return boolean true on success, false if address already used or invalid in some way
      */
     public function addBCC($address, $name = '')
     {
-        return $this->addAnAddress('bcc', $address, $name);
+        return $this->addOrEnqueueAnAddress('bcc', $address, $name);
     }
 
     /**
-     * Add a "Reply-to" address.
-     * @param string $address
+     * Add a "Reply-To" address.
+     * @param string $address The email address to reply to
      * @param string $name
-     * @return boolean
+     * @return boolean true on success, false if address already used or invalid in some way
      */
     public function addReplyTo($address, $name = '')
     {
-        return $this->addAnAddress('Reply-To', $address, $name);
+        return $this->addOrEnqueueAnAddress('Reply-To', $address, $name);
     }
 
     /**
-     * Add an address to one of the recipient arrays.
-     * Addresses that have been added already return false, but do not throw exceptions
-     * @param string $kind One of 'to', 'cc', 'bcc', 'ReplyTo'
-     * @param string $address The email address to send to
+     * Add an address to one of the recipient arrays or to the ReplyTo array. Because PHPMailer
+     * can't validate addresses with an IDN without knowing the PHPMailer::$CharSet (that can still
+     * be modified after calling this function), addition of such addresses is delayed until send().
+     * Addresses that have been added already return false, but do not throw exceptions.
+     * @param string $kind One of 'to', 'cc', 'bcc', or 'ReplyTo'
+     * @param string $address The email address to send, resp. to reply to
+     * @param string $name
+     * @throws phpmailerException
+     * @return boolean true on success, false if address already used or invalid in some way
+     * @access protected
+     */
+    protected function addOrEnqueueAnAddress($kind, $address, $name)
+    {
+        $address = trim($address);
+        $name = trim(preg_replace('/[\r\n]+/', '', $name)); //Strip breaks and trim
+        if (($pos = strrpos($address, '@')) === false) {
+            // At-sign is misssing.
+            $error_message = $this->lang('invalid_address') . " (addAnAddress $kind): $address";
+            $this->setError($error_message);
+            $this->edebug($error_message);
+            if ($this->exceptions) {
+                throw new phpmailerException($error_message);
+            }
+            return false;
+        }
+        $params = array($kind, $address, $name);
+        // Enqueue addresses with IDN until we know the PHPMailer::$CharSet.
+        if ($this->has8bitChars(substr($address, ++$pos)) and $this->idnSupported()) {
+            if ($kind != 'Reply-To') {
+                if (!array_key_exists($address, $this->RecipientsQueue)) {
+                    $this->RecipientsQueue[$address] = $params;
+                    return true;
+                }
+            } else {
+                if (!array_key_exists($address, $this->ReplyToQueue)) {
+                    $this->ReplyToQueue[$address] = $params;
+                    return true;
+                }
+            }
+            return false;
+        }
+        // Immediately add standard addresses without IDN.
+        return call_user_func_array(array($this, 'addAnAddress'), $params);
+    }
+
+    /**
+     * Add an address to one of the recipient arrays or to the ReplyTo array.
+     * Addresses that have been added already return false, but do not throw exceptions.
+     * @param string $kind One of 'to', 'cc', 'bcc', or 'ReplyTo'
+     * @param string $address The email address to send, resp. to reply to
      * @param string $name
      * @throws phpmailerException
      * @return boolean true on success, false if address already used or invalid in some way
@@ -819,26 +912,26 @@ class PHPMailer
      */
     protected function addAnAddress($kind, $address, $name = '')
     {
-        if (!preg_match('/^(to|cc|bcc|Reply-To)$/', $kind)) {
-            $this->setError($this->lang('Invalid recipient array') . ': ' . $kind);
-            $this->edebug($this->lang('Invalid recipient array') . ': ' . $kind);
+        if (!in_array($kind, array('to', 'cc', 'bcc', 'Reply-To'))) {
+            $error_message = $this->lang('Invalid recipient kind: ') . $kind;
+            $this->setError($error_message);
+            $this->edebug($error_message);
             if ($this->exceptions) {
-                throw new phpmailerException('Invalid recipient array: ' . $kind);
+                throw new phpmailerException($error_message);
             }
             return false;
         }
-        $address = trim($address);
-        $name = trim(preg_replace('/[\r\n]+/', '', $name)); //Strip breaks and trim
         if (!$this->validateAddress($address)) {
-            $this->setError($this->lang('invalid_address') . ': ' . $address);
-            $this->edebug($this->lang('invalid_address') . ': ' . $address);
+            $error_message = $this->lang('invalid_address') . " (addAnAddress $kind): $address";
+            $this->setError($error_message);
+            $this->edebug($error_message);
             if ($this->exceptions) {
-                throw new phpmailerException($this->lang('invalid_address') . ': ' . $address);
+                throw new phpmailerException($error_message);
             }
             return false;
         }
         if ($kind != 'Reply-To') {
-            if (!isset($this->all_recipients[strtolower($address)])) {
+            if (!array_key_exists(strtolower($address), $this->all_recipients)) {
                 array_push($this->$kind, array($address, $name));
                 $this->all_recipients[strtolower($address)] = true;
                 return true;
@@ -852,6 +945,61 @@ class PHPMailer
         return false;
     }
 
+    /**
+     * Parse and validate a string containing one or more RFC822-style comma-separated email addresses
+     * of the form "display name <address>" into an array of name/address pairs.
+     * Uses the imap_rfc822_parse_adrlist function if the IMAP extension is available.
+     * Note that quotes in the name part are removed.
+     * @param string $addrstr The address list string
+     * @param bool $useimap Whether to use the IMAP extension to parse the list
+     * @return array
+     * @link http://www.andrew.cmu.edu/user/agreen1/testing/mrbs/web/Mail/RFC822.php A more careful implementation
+     */
+    public function parseAddresses($addrstr, $useimap = true)
+    {
+        $addresses = array();
+        if ($useimap and function_exists('imap_rfc822_parse_adrlist')) {
+            //Use this built-in parser if it's available
+            $list = imap_rfc822_parse_adrlist($addrstr, '');
+            foreach ($list as $address) {
+                if ($address->host != '.SYNTAX-ERROR.') {
+                    if ($this->validateAddress($address->mailbox . '@' . $address->host)) {
+                        $addresses[] = array(
+                            'name' => (property_exists($address, 'personal') ? $address->personal : ''),
+                            'address' => $address->mailbox . '@' . $address->host
+                        );
+                    }
+                }
+            }
+        } else {
+            //Use this simpler parser
+            $list = explode(',', $addrstr);
+            foreach ($list as $address) {
+                $address = trim($address);
+                //Is there a separate name part?
+                if (strpos($address, '<') === false) {
+                    //No separate name, just use the whole thing
+                    if ($this->validateAddress($address)) {
+                        $addresses[] = array(
+                            'name' => '',
+                            'address' => $address
+                        );
+                    }
+                } else {
+                    list($name, $email) = explode('<', $address);
+                    $email = trim(str_replace('>', '', $email));
+                    if ($this->validateAddress($email)) {
+                        $addresses[] = array(
+                            'name' => trim(str_replace(array('"', "'"), '', $name)),
+                            'address' => $email
+                        );
+                    }
+                }
+            }
+        }
+        return $addresses;
+    }
+
     /**
      * Set the From and FromName properties.
      * @param string $address
@@ -864,11 +1012,15 @@ class PHPMailer
     {
         $address = trim($address);
         $name = trim(preg_replace('/[\r\n]+/', '', $name)); //Strip breaks and trim
-        if (!$this->validateAddress($address)) {
-            $this->setError($this->lang('invalid_address') . ': ' . $address);
-            $this->edebug($this->lang('invalid_address') . ': ' . $address);
+        // Don't validate now addresses with IDN. Will be done in send().
+        if (($pos = strrpos($address, '@')) === false or
+            (!$this->has8bitChars(substr($address, ++$pos)) or !$this->idnSupported()) and
+            !$this->validateAddress($address)) {
+            $error_message = $this->lang('invalid_address') . " (setFrom) $address";
+            $this->setError($error_message);
+            $this->edebug($error_message);
             if ($this->exceptions) {
-                throw new phpmailerException($this->lang('invalid_address') . ': ' . $address);
+                throw new phpmailerException($error_message);
             }
             return false;
         }
@@ -897,19 +1049,34 @@ class PHPMailer
     /**
      * Check that a string looks like an email address.
      * @param string $address The email address to check
-     * @param string $patternselect A selector for the validation pattern to use :
-     * * `auto` Pick strictest one automatically;
+     * @param string|callable $patternselect A selector for the validation pattern to use :
+     * * `auto` Pick best pattern automatically;
      * * `pcre8` Use the squiloople.com pattern, requires PCRE > 8.0, PHP >= 5.3.2, 5.2.14;
      * * `pcre` Use old PCRE implementation;
-     * * `php` Use PHP built-in FILTER_VALIDATE_EMAIL; same as pcre8 but does not allow 'dotless' domains;
+     * * `php` Use PHP built-in FILTER_VALIDATE_EMAIL;
      * * `html5` Use the pattern given by the HTML5 spec for 'email' type form input elements.
      * * `noregex` Don't use a regex: super fast, really dumb.
+     * Alternatively you may pass in a callable to inject your own validator, for example:
+     * PHPMailer::validateAddress('user@example.com', function($address) {
+     *     return (strpos($address, '@') !== false);
+     * });
+     * You can also set the PHPMailer::$validator static to a callable, allowing built-in methods to use your validator.
      * @return boolean
      * @static
      * @access public
      */
-    public static function validateAddress($address, $patternselect = 'auto')
+    public static function validateAddress($address, $patternselect = null)
     {
+        if (is_null($patternselect)) {
+            $patternselect = self::$validator;
+        }
+        if (is_callable($patternselect)) {
+            return call_user_func($patternselect, $address);
+        }
+        //Reject line breaks in addresses; it's valid RFC5322, but not RFC5321
+        if (strpos($address, "\n") !== false or strpos($address, "\r") !== false) {
+            return false;
+        }
         if (!$patternselect or $patternselect == 'auto') {
             //Check this constant first so it works when extension_loaded() is disabled by safe mode
             //Constant was added in PHP 5.2.4
@@ -989,6 +1156,48 @@ class PHPMailer
         }
     }
 
+    /**
+     * Tells whether IDNs (Internationalized Domain Names) are supported or not. This requires the
+     * "intl" and "mbstring" PHP extensions.
+     * @return bool "true" if required functions for IDN support are present
+     */
+    public function idnSupported()
+    {
+        // @TODO: Write our own "idn_to_ascii" function for PHP <= 5.2.
+        return function_exists('idn_to_ascii') and function_exists('mb_convert_encoding');
+    }
+
+    /**
+     * Converts IDN in given email address to its ASCII form, also known as punycode, if possible.
+     * Important: Address must be passed in same encoding as currently set in PHPMailer::$CharSet.
+     * This function silently returns unmodified address if:
+     * - No conversion is necessary (i.e. domain name is not an IDN, or is already in ASCII form)
+     * - Conversion to punycode is impossible (e.g. required PHP functions are not available)
+     *   or fails for any reason (e.g. domain has characters not allowed in an IDN)
+     * @see PHPMailer::$CharSet
+     * @param string $address The email address to convert
+     * @return string The encoded address in ASCII form
+     */
+    public function punyencodeAddress($address)
+    {
+        // Verify we have required functions, CharSet, and at-sign.
+        if ($this->idnSupported() and
+            !empty($this->CharSet) and
+            ($pos = strrpos($address, '@')) !== false) {
+            $domain = substr($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)) {
+                $domain = mb_convert_encoding($domain, 'UTF-8', $this->CharSet);
+                if (($punycode = defined('INTL_IDNA_VARIANT_UTS46') ?
+                    idn_to_ascii($domain, 0, INTL_IDNA_VARIANT_UTS46) :
+                    idn_to_ascii($domain)) !== false) {
+                    return substr($address, 0, $pos) . $punycode;
+                }
+            }
+        }
+        return $address;
+    }
+
     /**
      * Create a message and send it.
      * Uses the sending method specified by $Mailer.
@@ -1020,17 +1229,41 @@ class PHPMailer
     public function preSend()
     {
         try {
+            $this->error_count = 0; // Reset errors
             $this->mailHeader = '';
+
+            // Dequeue recipient and Reply-To addresses with IDN
+            foreach (array_merge($this->RecipientsQueue, $this->ReplyToQueue) as $params) {
+                $params[1] = $this->punyencodeAddress($params[1]);
+                call_user_func_array(array($this, 'addAnAddress'), $params);
+            }
             if ((count($this->to) + count($this->cc) + count($this->bcc)) < 1) {
                 throw new phpmailerException($this->lang('provide_address'), self::STOP_CRITICAL);
             }
 
+            // Validate From, Sender, and ConfirmReadingTo addresses
+            foreach (array('From', 'Sender', 'ConfirmReadingTo') as $address_kind) {
+                $this->$address_kind = trim($this->$address_kind);
+                if (empty($this->$address_kind)) {
+                    continue;
+                }
+                $this->$address_kind = $this->punyencodeAddress($this->$address_kind);
+                if (!$this->validateAddress($this->$address_kind)) {
+                    $error_message = $this->lang('invalid_address') . ' (punyEncode) ' . $this->$address_kind;
+                    $this->setError($error_message);
+                    $this->edebug($error_message);
+                    if ($this->exceptions) {
+                        throw new phpmailerException($error_message);
+                    }
+                    return false;
+                }
+            }
+
             // Set whether the message is multipart/alternative
-            if (!empty($this->AltBody)) {
+            if ($this->alternativeExists()) {
                 $this->ContentType = 'multipart/alternative';
             }
 
-            $this->error_count = 0; // Reset errors
             $this->setMessageType();
             // Refuse to send an empty message unless we are specifically allowing it
             if (!$this->AllowEmpty and empty($this->Body)) {
@@ -1061,9 +1294,11 @@ class PHPMailer
 
             // Sign with DKIM if enabled
             if (!empty($this->DKIM_domain)
-                && !empty($this->DKIM_private)
                 && !empty($this->DKIM_selector)
-                && file_exists($this->DKIM_private)) {
+                && (!empty($this->DKIM_private_string)
+                   || (!empty($this->DKIM_private) && file_exists($this->DKIM_private))
+                )
+            ) {
                 $header_dkim = $this->DKIM_Add(
                     $this->MIMEHeader . $this->mailHeader,
                     $this->encodeHeader($this->secureHeader($this->Subject)),
@@ -1129,19 +1364,24 @@ class PHPMailer
      */
     protected function sendmailSend($header, $body)
     {
-        if ($this->Sender != '') {
+        // 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 ($this->Mailer == 'qmail') {
-                $sendmail = sprintf('%s -f%s', escapeshellcmd($this->Sendmail), escapeshellarg($this->Sender));
+                $sendmailFmt = '%s -f%s';
             } else {
-                $sendmail = sprintf('%s -oi -f%s -t', escapeshellcmd($this->Sendmail), escapeshellarg($this->Sender));
+                $sendmailFmt = '%s -oi -f%s -t';
             }
         } else {
             if ($this->Mailer == 'qmail') {
-                $sendmail = sprintf('%s', escapeshellcmd($this->Sendmail));
+                $sendmailFmt = '%s';
             } else {
-                $sendmail = sprintf('%s -oi -t', escapeshellcmd($this->Sendmail));
+                $sendmailFmt = '%s -oi -t';
             }
         }
+
+        // TODO: If possible, this should be changed to escapeshellarg.  Needs thorough testing.
+        $sendmail = sprintf($sendmailFmt, escapeshellcmd($this->Sendmail), $this->Sender);
+
         if ($this->SingleTo) {
             foreach ($this->SingleToArray as $toAddr) {
                 if (!@$mail = popen($sendmail, 'w')) {
@@ -1171,7 +1411,15 @@ class PHPMailer
             fputs($mail, $header);
             fputs($mail, $body);
             $result = pclose($mail);
-            $this->doCallback(($result == 0), $this->to, $this->cc, $this->bcc, $this->Subject, $body, $this->From);
+            $this->doCallback(
+                ($result == 0),
+                $this->to,
+                $this->cc,
+                $this->bcc,
+                $this->Subject,
+                $body,
+                $this->From
+            );
             if ($result != 0) {
                 throw new phpmailerException($this->lang('execute') . $this->Sendmail, self::STOP_CRITICAL);
             }
@@ -1179,6 +1427,40 @@ class PHPMailer
         return true;
     }
 
+    /**
+     * Fix CVE-2016-10033 and CVE-2016-10045 by disallowing potentially unsafe shell characters.
+     *
+     * Note that escapeshellarg and escapeshellcmd are inadequate for our purposes, especially on Windows.
+     * @param string $string The string to be validated
+     * @see https://github.com/PHPMailer/PHPMailer/issues/924 CVE-2016-10045 bug report
+     * @access protected
+     * @return boolean
+     */
+    protected static function isShellSafe($string)
+    {
+        // Future-proof
+        if (escapeshellcmd($string) !== $string
+            or !in_array(escapeshellarg($string), array("'$string'", "\"$string\""))
+        ) {
+            return false;
+        }
+
+        $length = strlen($string);
+
+        for ($i = 0; $i < $length; $i++) {
+            $c = $string[$i];
+
+            // All other characters have a special meaning in at least one common shell, including = and +.
+            // Full stop (.) has a special meaning in cmd.exe, but its impact should be negligible here.
+            // Note that this does permit non-Latin alphanumeric characters based on the current locale.
+            if (!ctype_alnum($c) && strpos('@_-.', $c) === false) {
+                return false;
+            }
+        }
+
+        return true;
+    }
+
     /**
      * Send mail using the PHP mail() function.
      * @param string $header The message headers
@@ -1196,17 +1478,20 @@ class PHPMailer
         }
         $to = implode(', ', $toArr);
 
-        if (empty($this->Sender)) {
-            $params = ' ';
-        } else {
-            $params = sprintf('-f%s', $this->Sender);
+        $params = null;
+        //This sets the SMTP envelope sender which gets turned into a return-path header by the receiver
+        if (!empty($this->Sender) and $this->validateAddress($this->Sender)) {
+            // CVE-2016-10033, CVE-2016-10045: Don't pass -f if characters will be escaped.
+            if (self::isShellSafe($this->Sender)) {
+                $params = sprintf('-f%s', $this->Sender);
+            }
         }
-        if ($this->Sender != '' and !ini_get('safe_mode')) {
+        if (!empty($this->Sender) and !ini_get('safe_mode') and $this->validateAddress($this->Sender)) {
             $old_from = ini_get('sendmail_from');
             ini_set('sendmail_from', $this->Sender);
         }
         $result = false;
-        if ($this->SingleTo && count($toArr) > 1) {
+        if ($this->SingleTo and count($toArr) > 1) {
             foreach ($toArr as $toAddr) {
                 $result = $this->mailPassthru($toAddr, $this->Subject, $body, $header, $params);
                 $this->doCallback($result, array($toAddr), $this->cc, $this->bcc, $this->Subject, $body, $this->From);
@@ -1256,10 +1541,10 @@ class PHPMailer
         if (!$this->smtpConnect($this->SMTPOptions)) {
             throw new phpmailerException($this->lang('smtp_connect_failed'), self::STOP_CRITICAL);
         }
-        if ('' == $this->Sender) {
-            $smtp_from = $this->From;
-        } else {
+        if (!empty($this->Sender) and $this->validateAddress($this->Sender)) {
             $smtp_from = $this->Sender;
+        } else {
+            $smtp_from = $this->From;
         }
         if (!$this->smtp->mail($smtp_from)) {
             $this->setError($this->lang('from_failed') . $smtp_from . ' : ' . implode(',', $this->smtp->getError()));
@@ -1313,12 +1598,17 @@ class PHPMailer
      * @throws phpmailerException
      * @return boolean
      */
-    public function smtpConnect($options = array())
+    public function smtpConnect($options = null)
     {
         if (is_null($this->smtp)) {
             $this->smtp = $this->getSMTPInstance();
         }
 
+        //If no options are provided, use whatever is set in the instance
+        if (is_null($options)) {
+            $options = $this->SMTPOptions;
+        }
+
         // Already connected?
         if ($this->smtp->connected()) {
             return true;
@@ -1388,7 +1678,7 @@ class PHPMailer
                         if (!$this->smtp->startTLS()) {
                             throw new phpmailerException($this->lang('connect_host'));
                         }
-                        // We must resend HELO after tls negotiation
+                        // We must resend EHLO after TLS negotiation
                         $this->smtp->hello($hello);
                     }
                     if ($this->SMTPAuth) {
@@ -1427,7 +1717,7 @@ class PHPMailer
      */
     public function smtpClose()
     {
-        if ($this->smtp !== null) {
+        if (is_a($this->smtp, 'SMTP')) {
             if ($this->smtp->connected()) {
                 $this->smtp->quit();
                 $this->smtp->close();
@@ -1446,6 +1736,19 @@ class PHPMailer
      */
     public function setLanguage($langcode = 'en', $lang_path = '')
     {
+        // Backwards compatibility for renamed language codes
+        $renamed_langcodes = array(
+            'br' => 'pt_br',
+            'cz' => 'cs',
+            'dk' => 'da',
+            'no' => 'nb',
+            'se' => 'sv',
+        );
+
+        if (isset($renamed_langcodes[$langcode])) {
+            $langcode = $renamed_langcodes[$langcode];
+        }
+
         // Define full set of translatable strings in English
         $PHPMAILER_LANG = array(
             'authenticate' => 'SMTP Error: Could not authenticate.',
@@ -1458,7 +1761,7 @@ class PHPMailer
             'file_open' => 'File Error: Could not open file: ',
             'from_failed' => 'The following From address failed: ',
             'instantiate' => 'Could not instantiate mail function.',
-            'invalid_address' => 'Invalid address',
+            'invalid_address' => 'Invalid address: ',
             '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: ',
@@ -1472,6 +1775,10 @@ class PHPMailer
             // Calculate an absolute path so it can work if CWD is not here
             $lang_path = dirname(__FILE__). DIRECTORY_SEPARATOR . 'language'. DIRECTORY_SEPARATOR;
         }
+        //Validate $langcode
+        if (!preg_match('/^[a-z]{2}(?:_[a-zA-Z]{2})?$/', $langcode)) {
+            $langcode = 'en';
+        }
         $foundlang = true;
         $lang_file = $lang_path . 'phpmailer.lang-' . $langcode . '.php';
         // There is no English translation file
@@ -1723,7 +2030,6 @@ class PHPMailer
         }
         $result .= $this->headerLine('Date', $this->MessageDate);
 
-
         // To be created automatically by mail()
         if ($this->SingleTo) {
             if ($this->Mailer != 'mail') {
@@ -1766,17 +2072,21 @@ class PHPMailer
             $result .= $this->headerLine('Subject', $this->encodeHeader($this->secureHeader($this->Subject)));
         }
 
-        if ($this->MessageID != '') {
+        // 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)) {
             $this->lastMessageID = $this->MessageID;
         } else {
-            $this->lastMessageID = sprintf('<%s@%s>', $this->uniqueid, $this->ServerHostname());
+            $this->lastMessageID = sprintf('<%s@%s>', $this->uniqueid, $this->serverHostname());
         }
         $result .= $this->headerLine('Message-ID', $this->lastMessageID);
-        $result .= $this->headerLine('X-Priority', $this->Priority);
+        if (!is_null($this->Priority)) {
+            $result .= $this->headerLine('X-Priority', $this->Priority);
+        }
         if ($this->XMailer == '') {
             $result .= $this->headerLine(
                 'X-Mailer',
-                'PHPMailer ' . $this->Version . ' (https://github.com/PHPMailer/PHPMailer/)'
+                'PHPMailer ' . $this->Version . ' (https://github.com/PHPMailer/PHPMailer)'
             );
         } else {
             $myXmailer = trim($this->XMailer);
@@ -1786,7 +2096,7 @@ class PHPMailer
         }
 
         if ($this->ConfirmReadingTo != '') {
-            $result .= $this->headerLine('Disposition-Notification-To', '<' . trim($this->ConfirmReadingTo) . '>');
+            $result .= $this->headerLine('Disposition-Notification-To', '<' . $this->ConfirmReadingTo . '>');
         }
 
         // Add custom headers
@@ -1866,7 +2176,15 @@ class PHPMailer
      */
     public function getSentMIMEMessage()
     {
-        return $this->MIMEHeader . $this->mailHeader . self::CRLF . $this->MIMEBody;
+        return rtrim($this->MIMEHeader . $this->mailHeader, "\n\r") . self::CRLF . self::CRLF . $this->MIMEBody;
+    }
+
+    /**
+     * Create unique ID
+     * @return string
+     */
+    protected function generateId() {
+        return md5(uniqid(time()));
     }
 
     /**
@@ -1880,7 +2198,7 @@ class PHPMailer
     {
         $body = '';
         //Create unique IDs and preset boundaries
-        $this->uniqueid = md5(uniqid(time()));
+        $this->uniqueid = $this->generateId();
         $this->boundary[1] = 'b1_' . $this->uniqueid;
         $this->boundary[2] = 'b2_' . $this->uniqueid;
         $this->boundary[3] = 'b3_' . $this->uniqueid;
@@ -1896,11 +2214,12 @@ class PHPMailer
         //Can we do a 7-bit downgrade?
         if ($bodyEncoding == '8bit' and !$this->has8bitChars($this->Body)) {
             $bodyEncoding = '7bit';
+            //All ISO 8859, Windows codepage and UTF-8 charsets are ascii compatible up to 7-bit
             $bodyCharSet = 'us-ascii';
         }
-        //If lines are too long, change to quoted-printable transfer encoding
-        if (self::hasLineLongerThanMax($this->Body)) {
-            $this->Encoding = 'quoted-printable';
+        //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 ('base64' != $this->Encoding and self::hasLineLongerThanMax($this->Body)) {
             $bodyEncoding = 'quoted-printable';
         }
 
@@ -1909,10 +2228,12 @@ class PHPMailer
         //Can we do a 7-bit downgrade?
         if ($altBodyEncoding == '8bit' and !$this->has8bitChars($this->AltBody)) {
             $altBodyEncoding = '7bit';
+            //All ISO 8859, Windows codepage and UTF-8 charsets are ascii compatible up to 7-bit
             $altBodyCharSet = 'us-ascii';
         }
-        //If lines are too long, change to quoted-printable transfer encoding
-        if (self::hasLineLongerThanMax($this->AltBody)) {
+        //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 ('base64' != $altBodyEncoding and self::hasLineLongerThanMax($this->AltBody)) {
             $altBodyEncoding = 'quoted-printable';
         }
         //Use this as a preamble in all multipart message types
@@ -2015,8 +2336,10 @@ class PHPMailer
                 $body .= $this->attachAll('attachment', $this->boundary[1]);
                 break;
             default:
-                // catch case 'plain' and case ''
-                $body .= $this->encodeString($this->Body, $bodyEncoding);
+                // Catch case 'plain' and case '', applies to simple `text/plain` and `text/html` body content types
+                //Reset the `Encoding` property in case we changed it for line length reasons
+                $this->Encoding = $bodyEncoding;
+                $body .= $this->encodeString($this->Body, $this->Encoding);
                 break;
         }
 
@@ -2122,8 +2445,7 @@ class PHPMailer
 
     /**
      * Set the message type.
-     * PHPMailer only supports some preset message types,
-     * not arbitrary MIME structures.
+     * PHPMailer only supports some preset message types, not arbitrary MIME structures.
      * @access protected
      * @return void
      */
@@ -2141,6 +2463,7 @@ class PHPMailer
         }
         $this->message_type = implode('_', $type);
         if ($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';
         }
     }
@@ -2266,18 +2589,27 @@ class PHPMailer
                 $type = $attachment[4];
                 $disposition = $attachment[6];
                 $cid = $attachment[7];
-                if ($disposition == 'inline' && isset($cidUniq[$cid])) {
+                if ($disposition == 'inline' && array_key_exists($cid, $cidUniq)) {
                     continue;
                 }
                 $cidUniq[$cid] = true;
 
                 $mime[] = sprintf('--%s%s', $boundary, $this->LE);
-                $mime[] = sprintf(
-                    'Content-Type: %s; name="%s"%s',
-                    $type,
-                    $this->encodeHeader($this->secureHeader($name)),
-                    $this->LE
-                );
+                //Only include a filename property if we have one
+                if (!empty($name)) {
+                    $mime[] = sprintf(
+                        'Content-Type: %s; name="%s"%s',
+                        $type,
+                        $this->encodeHeader($this->secureHeader($name)),
+                        $this->LE
+                    );
+                } else {
+                    $mime[] = sprintf(
+                        'Content-Type: %s%s',
+                        $type,
+                        $this->LE
+                    );
+                }
                 // RFC1341 part 5 says 7bit is assumed if not specified
                 if ($encoding != '7bit') {
                     $mime[] = sprintf('Content-Transfer-Encoding: %s%s', $encoding, $this->LE);
@@ -2301,12 +2633,20 @@ class PHPMailer
                             $this->LE . $this->LE
                         );
                     } else {
-                        $mime[] = sprintf(
-                            'Content-Disposition: %s; filename=%s%s',
-                            $disposition,
-                            $encoded_name,
-                            $this->LE . $this->LE
-                        );
+                        if (!empty($encoded_name)) {
+                            $mime[] = sprintf(
+                                'Content-Disposition: %s; filename=%s%s',
+                                $disposition,
+                                $encoded_name,
+                                $this->LE . $this->LE
+                            );
+                        } else {
+                            $mime[] = sprintf(
+                                'Content-Disposition: %s%s',
+                                $disposition,
+                                $this->LE . $this->LE
+                            );
+                        }
                     }
                 } else {
                     $mime[] = $this->LE;
@@ -2340,7 +2680,6 @@ 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 phpmailerException
-     * @see EncodeFile(encodeFile
      * @access protected
      * @return string
      */
@@ -2560,7 +2899,7 @@ class PHPMailer
     {
         // Use native function if it's available (>= PHP5.3)
         if (function_exists('quoted_printable_encode')) {
-            return $this->fixEOL(quoted_printable_encode($string));
+            return quoted_printable_encode($string);
         }
         // Fall back to a pure PHP implementation
         $string = str_replace(
@@ -2568,8 +2907,7 @@ class PHPMailer
             array(' ', "\r\n=2E", "\r\n", '='),
             rawurlencode($string)
         );
-        $string = preg_replace('/[^\r\n]{' . ($line_max - 3) . '}[^=\r\n]{2}/', "$0=\r\n", $string);
-        return $this->fixEOL($string);
+        return preg_replace('/[^\r\n]{' . ($line_max - 3) . '}[^=\r\n]{2}/', "$0=\r\n", $string);
     }
 
     /**
@@ -2638,7 +2976,6 @@ class PHPMailer
         return str_replace(' ', '_', $encoded);
     }
 
-
     /**
      * Add a string or binary attachment (non-filesystem).
      * This method can be used to attach ascii or binary data,
@@ -2744,7 +3081,7 @@ class PHPMailer
         $disposition = 'inline'
     ) {
         // If a MIME type is not specified, try to work it out from the name
-        if ($type == '') {
+        if ($type == '' and !empty($name)) {
             $type = self::filenameToType($name);
         }
 
@@ -2800,6 +3137,22 @@ class PHPMailer
         return !empty($this->AltBody);
     }
 
+    /**
+     * Clear queued addresses of given kind.
+     * @access protected
+     * @param string $kind 'to', 'cc', or 'bcc'
+     * @return void
+     */
+    public function clearQueuedAddresses($kind)
+    {
+        $RecipientsQueue = $this->RecipientsQueue;
+        foreach ($RecipientsQueue as $address => $params) {
+            if ($params[0] == $kind) {
+                unset($this->RecipientsQueue[$address]);
+            }
+        }
+    }
+
     /**
      * Clear all To recipients.
      * @return void
@@ -2810,6 +3163,7 @@ class PHPMailer
             unset($this->all_recipients[strtolower($to[0])]);
         }
         $this->to = array();
+        $this->clearQueuedAddresses('to');
     }
 
     /**
@@ -2822,6 +3176,7 @@ class PHPMailer
             unset($this->all_recipients[strtolower($cc[0])]);
         }
         $this->cc = array();
+        $this->clearQueuedAddresses('cc');
     }
 
     /**
@@ -2834,6 +3189,7 @@ class PHPMailer
             unset($this->all_recipients[strtolower($bcc[0])]);
         }
         $this->bcc = array();
+        $this->clearQueuedAddresses('bcc');
     }
 
     /**
@@ -2843,6 +3199,7 @@ class PHPMailer
     public function clearReplyTos()
     {
         $this->ReplyTo = array();
+        $this->ReplyToQueue = array();
     }
 
     /**
@@ -2855,6 +3212,7 @@ class PHPMailer
         $this->cc = array();
         $this->bcc = array();
         $this->all_recipients = array();
+        $this->RecipientsQueue = array();
     }
 
     /**
@@ -3011,8 +3369,7 @@ class PHPMailer
     }
 
     /**
-     * Returns all custom headers
-     *
+     * Returns all custom headers.
      * @return array
      */
     public function getCustomHeaders()
@@ -3021,21 +3378,23 @@ class PHPMailer
     }
 
     /**
-     * Create a message from an HTML string.
-     * Automatically makes modifications for inline images and backgrounds
-     * and creates a plain-text version by converting the HTML.
-     * Overwrites any existing values in $this->Body and $this->AltBody
+     * Create a message body from an HTML string.
+     * Automatically inlines images and creates a plain-text version by converting the HTML,
+     * overwriting any existing values in Body and AltBody.
+     * $basedir is used when handling relative image paths, e.g. <img src="images/a.png">
+     * will look for an image file in $basedir/images/a.png and convert it to inline.
+     * If you don't want to apply these transformations to your HTML, just set Body and AltBody yourself.
      * @access public
      * @param string $message HTML message string
-     * @param string $basedir baseline directory for path
+     * @param string $basedir base directory for relative paths to images
      * @param boolean|callable $advanced Whether to use the internal HTML to text converter
-     *    or your own custom converter @see html2text()
-     * @return string $message
+     *    or your own custom converter @see PHPMailer::html2text()
+     * @return string $message The transformed message Body
      */
     public function msgHTML($message, $basedir = '', $advanced = false)
     {
         preg_match_all('/(src|background)=["\'](.*)["\']/Ui', $message, $images);
-        if (isset($images[2])) {
+        if (array_key_exists(2, $images)) {
             foreach ($images[2] as $imgindex => $url) {
                 // Convert data URIs into embedded images
                 if (preg_match('#^data:(image[^;,]*)(;base64)?,#', $url, $match)) {
@@ -3046,15 +3405,16 @@ class PHPMailer
                         $data = rawurldecode($data);
                     }
                     $cid = md5($url) . '@phpmailer.0'; // RFC2392 S 2
-                    if ($this->addStringEmbeddedImage($data, $cid, '', 'base64', $match[1])) {
+                    if ($this->addStringEmbeddedImage($data, $cid, 'embed' . $imgindex, 'base64', $match[1])) {
                         $message = str_replace(
                             $images[0][$imgindex],
                             $images[1][$imgindex] . '="cid:' . $cid . '"',
                             $message
                         );
                     }
-                } elseif (!preg_match('#^[A-z]+://#', $url)) {
+                } elseif (substr($url, 0, 4) !== 'cid:' && !preg_match('#^[a-z][a-z0-9+.-]*://#i', $url)) {
                     // Do not change urls for absolute images (thanks to corvuscorax)
+                    // Do not change urls that are already inline images
                     $filename = basename($url);
                     $directory = dirname($url);
                     if ($directory == '.') {
@@ -3088,7 +3448,7 @@ class PHPMailer
         // Convert all message body line breaks to CRLF, makes quoted-printable encoding work much better
         $this->Body = $this->normalizeBreaks($message);
         $this->AltBody = $this->normalizeBreaks($this->html2text($message, $advanced));
-        if (empty($this->AltBody)) {
+        if (!$this->alternativeExists()) {
             $this->AltBody = 'To view this email message, open it in a program that understands HTML!' .
                 self::CRLF . self::CRLF;
         }
@@ -3099,7 +3459,7 @@ class PHPMailer
      * Convert an HTML string into plain text.
      * This is used by msgHTML().
      * Note - older versions of this function used a bundled advanced converter
-     * which was been removed for license reasons in #232
+     * which was been removed for license reasons in #232.
      * Example usage:
      * <code>
      * // Use default conversion
@@ -3144,6 +3504,16 @@ class PHPMailer
             'bin'   => 'application/macbinary',
             'doc'   => 'application/msword',
             'word'  => 'application/msword',
+            'xlsx'  => 'application/vnd.openxmlformats-officedocument.spreadsheetml.sheet',
+            'xltx'  => 'application/vnd.openxmlformats-officedocument.spreadsheetml.template',
+            'potx'  => 'application/vnd.openxmlformats-officedocument.presentationml.template',
+            'ppsx'  => 'application/vnd.openxmlformats-officedocument.presentationml.slideshow',
+            'pptx'  => 'application/vnd.openxmlformats-officedocument.presentationml.presentation',
+            'sldx'  => 'application/vnd.openxmlformats-officedocument.presentationml.slide',
+            'docx'  => 'application/vnd.openxmlformats-officedocument.wordprocessingml.document',
+            'dotx'  => 'application/vnd.openxmlformats-officedocument.wordprocessingml.template',
+            'xlam'  => 'application/vnd.ms-excel.addin.macroEnabled.12',
+            'xlsb'  => 'application/vnd.ms-excel.sheet.binary.macroEnabled.12',
             'class' => 'application/octet-stream',
             'dll'   => 'application/octet-stream',
             'dms'   => 'application/octet-stream',
@@ -3348,7 +3718,6 @@ class PHPMailer
         return preg_replace('/(\r\n|\r|\n)/ms', $breaktype, $text);
     }
 
-
     /**
      * Set the public and private key files and password for S/MIME signing.
      * @access public
@@ -3390,7 +3759,7 @@ class PHPMailer
      * @access public
      * @param string $signHeader
      * @throws phpmailerException
-     * @return string
+     * @return string The DKIM signature value
      */
     public function DKIM_Sign($signHeader)
     {
@@ -3400,15 +3769,35 @@ class PHPMailer
             }
             return '';
         }
-        $privKeyStr = file_get_contents($this->DKIM_private);
-        if ($this->DKIM_passphrase != '') {
+        $privKeyStr = !empty($this->DKIM_private_string) ? $this->DKIM_private_string : file_get_contents($this->DKIM_private);
+        if ('' != $this->DKIM_passphrase) {
             $privKey = openssl_pkey_get_private($privKeyStr, $this->DKIM_passphrase);
         } else {
-            $privKey = $privKeyStr;
+            $privKey = openssl_pkey_get_private($privKeyStr);
         }
-        if (openssl_sign($signHeader, $signature, $privKey)) {
-            return base64_encode($signature);
+        //Workaround for missing digest algorithms in old PHP & OpenSSL versions
+        //@link http://stackoverflow.com/a/11117338/333340
+        if (version_compare(PHP_VERSION, '5.3.0') >= 0 and
+            in_array('sha256WithRSAEncryption', openssl_get_md_methods(true))) {
+            if (openssl_sign($signHeader, $signature, $privKey, 'sha256WithRSAEncryption')) {
+                openssl_pkey_free($privKey);
+                return base64_encode($signature);
+            }
+        } else {
+            $pinfo = openssl_pkey_get_details($privKey);
+            $hash = hash('sha256', $signHeader);
+            //'Magic' constant for SHA256 from RFC3447
+            //@link https://tools.ietf.org/html/rfc3447#page-43
+            $t = '3031300d060960864801650304020105000420' . $hash;
+            $pslen = $pinfo['bits'] / 8 - (strlen($t) / 2 + 3);
+            $eb = pack('H*', '0001' . str_repeat('FF', $pslen) . '00' . $t);
+
+            if (openssl_private_encrypt($eb, $signature, $privKey, OPENSSL_NO_PADDING)) {
+                openssl_pkey_free($privKey);
+                return base64_encode($signature);
+            }
         }
+        openssl_pkey_free($privKey);
         return '';
     }
 
@@ -3425,7 +3814,7 @@ class PHPMailer
         foreach ($lines as $key => $line) {
             list($heading, $value) = explode(':', $line, 2);
             $heading = strtolower($heading);
-            $value = preg_replace('/\s+/', ' ', $value); // Compress useless spaces
+            $value = preg_replace('/\s{2,}/', ' ', $value); // Compress useless spaces
             $lines[$key] = $heading . ':' . trim($value); // Don't forget to remove WSP around the value
         }
         $signHeader = implode("\r\n", $lines);
@@ -3463,7 +3852,7 @@ class PHPMailer
      */
     public function DKIM_Add($headers_line, $subject, $body)
     {
-        $DKIMsignatureType = 'rsa-sha1'; // Signature & hash algorithms
+        $DKIMsignatureType = 'rsa-sha256'; // Signature & hash algorithms
         $DKIMcanonicalization = 'relaxed/simple'; // Canonicalization of header/body
         $DKIMquery = 'dns/txt'; // Query method
         $DKIMtime = time(); // Signature Timestamp = seconds since 00:00:00 - Jan 1, 1970 (UTC time zone)
@@ -3471,6 +3860,7 @@ class PHPMailer
         $headers = explode($this->LE, $headers_line);
         $from_header = '';
         $to_header = '';
+        $date_header = '';
         $current = '';
         foreach ($headers as $header) {
             if (strpos($header, 'From:') === 0) {
@@ -3479,6 +3869,9 @@ class PHPMailer
             } elseif (strpos($header, 'To:') === 0) {
                 $to_header = $header;
                 $current = 'to_header';
+            } elseif (strpos($header, 'Date:') === 0) {
+                $date_header = $header;
+                $current = 'date_header';
             } else {
                 if (!empty($$current) && strpos($header, ' =?') === 0) {
                     $$current .= $header;
@@ -3489,6 +3882,7 @@ class PHPMailer
         }
         $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',
@@ -3496,7 +3890,7 @@ class PHPMailer
         ); // Copied header fields (dkim-quoted-printable)
         $body = $this->DKIM_BodyC($body);
         $DKIMlen = strlen($body); // Length of body
-        $DKIMb64 = base64_encode(pack('H*', sha1($body))); // Base64 of packed binary SHA-1 hash 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 {
@@ -3509,15 +3903,20 @@ class PHPMailer
             $this->DKIM_selector .
             ";\r\n" .
             "\tt=" . $DKIMtime . '; c=' . $DKIMcanonicalization . ";\r\n" .
-            "\th=From:To:Subject;\r\n" .
+            "\th=From:To:Date:Subject;\r\n" .
             "\td=" . $this->DKIM_domain . ';' . $ident . "\r\n" .
             "\tz=$from\r\n" .
             "\t|$to\r\n" .
+            "\t|$date\r\n" .
             "\t|$subject;\r\n" .
             "\tbh=" . $DKIMb64 . ";\r\n" .
             "\tb=";
         $toSign = $this->DKIM_HeaderC(
-            $from_header . "\r\n" . $to_header . "\r\n" . $subject_header . "\r\n" . $dkimhdrs
+            $from_header . "\r\n" .
+            $to_header . "\r\n" .
+            $date_header . "\r\n" .
+            $subject_header . "\r\n" .
+            $dkimhdrs
         );
         $signed = $this->DKIM_Sign($toSign);
         return $dkimhdrs . $signed . "\r\n";
@@ -3537,6 +3936,7 @@ class PHPMailer
 
     /**
      * Allows for public read access to 'to' property.
+     * @note: Before the send() call, queued addresses (i.e. with IDN) are not yet included.
      * @access public
      * @return array
      */
@@ -3547,6 +3947,7 @@ class PHPMailer
 
     /**
      * Allows for public read access to 'cc' property.
+     * @note: Before the send() call, queued addresses (i.e. with IDN) are not yet included.
      * @access public
      * @return array
      */
@@ -3557,6 +3958,7 @@ class PHPMailer
 
     /**
      * Allows for public read access to 'bcc' property.
+     * @note: Before the send() call, queued addresses (i.e. with IDN) are not yet included.
      * @access public
      * @return array
      */
@@ -3567,6 +3969,7 @@ class PHPMailer
 
     /**
      * Allows for public read access to 'ReplyTo' property.
+     * @note: Before the send() call, queued addresses (i.e. with IDN) are not yet included.
      * @access public
      * @return array
      */
@@ -3577,6 +3980,7 @@ class PHPMailer
 
     /**
      * Allows for public read access to 'all_recipients' property.
+     * @note: Before the send() call, queued addresses (i.e. with IDN) are not yet included.
      * @access public
      * @return array
      */
diff --git a/wp-includes/class-smtp.php b/wp-includes/class-smtp.php
index 1eae77a128..3aa48f4fb0 100644
--- a/wp-includes/class-smtp.php
+++ b/wp-includes/class-smtp.php
@@ -28,25 +28,25 @@ class SMTP
 {
     /**
      * The PHPMailer SMTP version number.
-     * @type string
+     * @var string
      */
-    const VERSION = '5.2.10';
+    const VERSION = '5.2.21';
 
     /**
      * SMTP line break constant.
-     * @type string
+     * @var string
      */
     const CRLF = "\r\n";
 
     /**
      * The SMTP port to use if one is not specified.
-     * @type integer
+     * @var integer
      */
     const DEFAULT_SMTP_PORT = 25;
 
     /**
      * The maximum line length allowed by RFC 2822 section 2.1.1
-     * @type integer
+     * @var integer
      */
     const MAX_LINE_LENGTH = 998;
 
@@ -77,15 +77,15 @@ class SMTP
 
     /**
      * The PHPMailer SMTP Version number.
-     * @type string
+     * @var string
      * @deprecated Use the `VERSION` constant instead
      * @see SMTP::VERSION
      */
-    public $Version = '5.2.10';
+    public $Version = '5.2.21';
 
     /**
      * SMTP server port number.
-     * @type integer
+     * @var integer
      * @deprecated This is only ever used as a default value, so use the `DEFAULT_SMTP_PORT` constant instead
      * @see SMTP::DEFAULT_SMTP_PORT
      */
@@ -93,7 +93,7 @@ class SMTP
 
     /**
      * SMTP reply line ending.
-     * @type string
+     * @var string
      * @deprecated Use the `CRLF` constant instead
      * @see SMTP::CRLF
      */
@@ -107,7 +107,7 @@ class SMTP
      * * self::DEBUG_SERVER (`2`) Client commands and server responses
      * * self::DEBUG_CONNECTION (`3`) As DEBUG_SERVER plus connection status
      * * self::DEBUG_LOWLEVEL (`4`) Low-level data output, all messages
-     * @type integer
+     * @var integer
      */
     public $do_debug = self::DEBUG_OFF;
 
@@ -122,7 +122,7 @@ class SMTP
      * <code>
      * $smtp->Debugoutput = function($str, $level) {echo "debug level $level; message: $str";};
      * </code>
-     * @type string|callable
+     * @var string|callable
      */
     public $Debugoutput = 'echo';
 
@@ -130,7 +130,7 @@ class SMTP
      * Whether to use VERP.
      * @link http://en.wikipedia.org/wiki/Variable_envelope_return_path
      * @link http://www.postfix.org/VERP_README.html Info on VERP
-     * @type boolean
+     * @var boolean
      */
     public $do_verp = false;
 
@@ -139,26 +139,37 @@ class SMTP
      * Default of 5 minutes (300sec) is from RFC2821 section 4.5.3.2
      * This needs to be quite high to function correctly with hosts using greetdelay as an anti-spam measure.
      * @link http://tools.ietf.org/html/rfc2821#section-4.5.3.2
-     * @type integer
+     * @var integer
      */
     public $Timeout = 300;
 
     /**
      * How long to wait for commands to complete, in seconds.
      * Default of 5 minutes (300sec) is from RFC2821 section 4.5.3.2
-     * @type integer
+     * @var integer
      */
     public $Timelimit = 300;
 
+	/**
+	 * @var array patterns to extract smtp transaction id from smtp reply
+	 * Only first capture group will be use, use non-capturing group to deal with it
+	 * Extend this class to override this property to fulfil your needs.
+	 */
+	protected $smtp_transaction_id_patterns = array(
+		'exim' => '/[0-9]{3} OK id=(.*)/',
+		'sendmail' => '/[0-9]{3} 2.0.0 (.*) Message/',
+		'postfix' => '/[0-9]{3} 2.0.0 Ok: queued as (.*)/'
+	);
+
     /**
      * The socket for the server connection.
-     * @type resource
+     * @var resource
      */
     protected $smtp_conn;
 
     /**
      * Error information, if any, for the last SMTP command.
-     * @type array
+     * @var array
      */
     protected $error = array(
         'error' => '',
@@ -170,7 +181,7 @@ class SMTP
     /**
      * The reply the server sent to us for HELO.
      * If null, no HELO string has yet been received.
-     * @type string|null
+     * @var string|null
      */
     protected $helo_rply = null;
 
@@ -181,13 +192,13 @@ class SMTP
      * represents the server name. In case of HELO it is the only element of the array.
      * Other values can be boolean TRUE or an array containing extension options.
      * If null, no HELO/EHLO string has yet been received.
-     * @type array|null
+     * @var array|null
      */
     protected $server_caps = null;
 
     /**
      * The most recent reply received from the server.
-     * @type string
+     * @var string
      */
     protected $last_reply = '';
 
@@ -206,7 +217,7 @@ class SMTP
         }
         //Avoid clash with built-in function names
         if (!in_array($this->Debugoutput, array('error_log', 'html', 'echo')) and is_callable($this->Debugoutput)) {
-            call_user_func($this->Debugoutput, $str, $this->do_debug);
+            call_user_func($this->Debugoutput, $str, $level);
             return;
         }
         switch ($this->Debugoutput) {
@@ -272,8 +283,8 @@ class SMTP
         $errstr = '';
         if ($streamok) {
             $socket_context = stream_context_create($options);
-            //Suppress errors; connection failures are handled at a higher level
-            $this->smtp_conn = @stream_socket_client(
+            set_error_handler(array($this, 'errorHandler'));
+            $this->smtp_conn = stream_socket_client(
                 $host . ":" . $port,
                 $errno,
                 $errstr,
@@ -281,12 +292,14 @@ 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
             $this->edebug(
                 "Connection: stream_socket_client not available, falling back to fsockopen",
                 self::DEBUG_CONNECTION
             );
+            set_error_handler(array($this, 'errorHandler'));
             $this->smtp_conn = fsockopen(
                 $host,
                 $port,
@@ -294,6 +307,7 @@ class SMTP
                 $errstr,
                 $timeout
             );
+            restore_error_handler();
         }
         // Verify we connected properly
         if (!is_resource($this->smtp_conn)) {
@@ -336,11 +350,22 @@ class SMTP
         if (!$this->sendCommand('STARTTLS', 'STARTTLS', 220)) {
             return false;
         }
+
+        //Allow the best TLS version(s) we can
+        $crypto_method = STREAM_CRYPTO_METHOD_TLS_CLIENT;
+
+        //PHP 5.6.7 dropped inclusion of TLS 1.1 and 1.2 in STREAM_CRYPTO_METHOD_TLS_CLIENT
+        //so add them back in manually if we can
+        if (defined('STREAM_CRYPTO_METHOD_TLSv1_2_CLIENT')) {
+            $crypto_method |= STREAM_CRYPTO_METHOD_TLSv1_2_CLIENT;
+            $crypto_method |= STREAM_CRYPTO_METHOD_TLSv1_1_CLIENT;
+        }
+
         // Begin encrypted connection
         if (!stream_socket_enable_crypto(
             $this->smtp_conn,
             true,
-            STREAM_CRYPTO_METHOD_TLS_CLIENT
+            $crypto_method
         )) {
             return false;
         }
@@ -351,20 +376,21 @@ class SMTP
      * Perform SMTP authentication.
      * Must be run after hello().
      * @see hello()
-     * @param string $username    The user name
-     * @param string $password    The password
-     * @param string $authtype    The auth type (PLAIN, LOGIN, NTLM, CRAM-MD5)
-     * @param string $realm       The auth realm for NTLM
+     * @param string $username The user name
+     * @param string $password The password
+     * @param string $authtype The auth type (PLAIN, LOGIN, CRAM-MD5)
+     * @param string $realm The auth realm for NTLM
      * @param string $workstation The auth workstation for NTLM
-     * @access public
-     * @return boolean True if successfully authenticated.
+     * @param null|OAuth $OAuth An optional OAuth instance (@see PHPMailerOAuth)
+     * @return bool True if successfully authenticated.* @access public
      */
     public function authenticate(
         $username,
         $password,
         $authtype = null,
         $realm = '',
-        $workstation = ''
+        $workstation = '',
+        $OAuth = null
     ) {
         if (!$this->server_caps) {
             $this->setError('Authentication is not allowed before HELO/EHLO');
@@ -388,7 +414,7 @@ class SMTP
             );
 
             if (empty($authtype)) {
-                foreach (array('LOGIN', 'CRAM-MD5', 'PLAIN') as $method) {
+                foreach (array('CRAM-MD5', 'LOGIN', 'PLAIN') as $method) {
                     if (in_array($method, $this->server_caps['AUTH'])) {
                         $authtype = $method;
                         break;
@@ -672,10 +698,12 @@ class SMTP
     protected function parseHelloFields($type)
     {
         $this->server_caps = array();
-        $lines = explode("\n", $this->last_reply);
+        $lines = explode("\n", $this->helo_rply);
+
         foreach ($lines as $n => $s) {
+            //First 4 chars contain response code followed by - or space
             $s = trim(substr($s, 4));
-            if (!$s) {
+            if (empty($s)) {
                 continue;
             }
             $fields = explode(' ', $s);
@@ -685,11 +713,20 @@ class SMTP
                     $fields = $fields[0];
                 } else {
                     $name = array_shift($fields);
-                    if ($name == 'SIZE') {
-                        $fields = ($fields) ? $fields[0] : 0;
+                    switch ($name) {
+                        case 'SIZE':
+                            $fields = ($fields ? $fields[0] : 0);
+                            break;
+                        case 'AUTH':
+                            if (!is_array($fields)) {
+                                $fields = array();
+                            }
+                            break;
+                        default:
+                            $fields = true;
                     }
                 }
-                $this->server_caps[$name] = ($fields ? $fields : true);
+                $this->server_caps[$name] = $fields;
             }
         }
     }
@@ -739,15 +776,15 @@ class SMTP
      * Sets the TO argument to $toaddr.
      * Returns true if the recipient was accepted false if it was rejected.
      * Implements from rfc 821: RCPT <SP> TO:<forward-path> <CRLF>
-     * @param string $toaddr The address the message is being sent to
+     * @param string $address The address the message is being sent to
      * @access public
      * @return boolean
      */
-    public function recipient($toaddr)
+    public function recipient($address)
     {
         return $this->sendCommand(
             'RCPT TO',
-            'RCPT TO:<' . $toaddr . '>',
+            'RCPT TO:<' . $address . '>',
             array(250, 251)
         );
     }
@@ -766,9 +803,9 @@ class SMTP
 
     /**
      * Send a command to an SMTP server and check its return code.
-     * @param string $command       The command name - not sent to the server
+     * @param string $command The command name - not sent to the server
      * @param string $commandstring The actual command to send
-     * @param integer|array $expect     One or more expected integer success codes
+     * @param integer|array $expect One or more expected integer success codes
      * @access protected
      * @return boolean True on success.
      */
@@ -778,6 +815,11 @@ class SMTP
             $this->setError("Called $command without being connected");
             return false;
         }
+        //Reject line breaks in all commands
+        if (strpos($commandstring, "\n") !== false or strpos($commandstring, "\r") !== false) {
+            $this->setError("Command '$command' contained line breaks");
+            return false;
+        }
         $this->client_send($commandstring . self::CRLF);
 
         $this->last_reply = $this->get_lines();
@@ -981,10 +1023,9 @@ class SMTP
         }
         while (is_resource($this->smtp_conn) && !feof($this->smtp_conn)) {
             $str = @fgets($this->smtp_conn, 515);
-            $this->edebug("SMTP -> get_lines(): \$data was \"$data\"", self::DEBUG_LOWLEVEL);
-            $this->edebug("SMTP -> get_lines(): \$str is \"$str\"", self::DEBUG_LOWLEVEL);
-            $data .= $str;
             $this->edebug("SMTP -> get_lines(): \$data is \"$data\"", self::DEBUG_LOWLEVEL);
+            $this->edebug("SMTP -> get_lines(): \$str is  \"$str\"", self::DEBUG_LOWLEVEL);
+            $data .= $str;
             // If 4th character is a space, we are done reading, break the loop, micro-optimisation over strlen
             if ((isset($str[3]) and $str[3] == ' ')) {
                 break;
@@ -1099,4 +1140,47 @@ class SMTP
     {
         return $this->Timeout;
     }
+
+    /**
+     * Reports an error number and string.
+     * @param integer $errno The error number returned by PHP.
+     * @param string $errmsg The error message returned by PHP.
+     */
+    protected function errorHandler($errno, $errmsg)
+    {
+        $notice = 'Connection: Failed to connect to server.';
+        $this->setError(
+            $notice,
+            $errno,
+            $errmsg
+        );
+        $this->edebug(
+            $notice . ' Error number ' . $errno . '. "Error notice: ' . $errmsg,
+            self::DEBUG_CONNECTION
+        );
+    }
+
+	/**
+	 * Will return the ID of the last smtp transaction based on a list of patterns provided
+	 * in SMTP::$smtp_transaction_id_patterns.
+	 * If no reply has been received yet, it will return null.
+	 * If no pattern has been matched, it will return false.
+	 * @return bool|null|string
+	 */
+	public function getLastTransactionID()
+	{
+		$reply = $this->getLastReply();
+
+		if (empty($reply)) {
+			return null;
+		}
+
+		foreach($this->smtp_transaction_id_patterns as $smtp_transaction_id_pattern) {
+			if(preg_match($smtp_transaction_id_pattern, $reply, $matches)) {
+				return $matches[1];
+			}
+		}
+
+		return false;
+    }
 }