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<?php

/**

 * PHPMailer RFC821 SMTP email 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;

/**

 * PHPMailer RFC821 SMTP email transport class.

 * Implements RFC 821 SMTP commands and provides some utility methods for sending mail to an SMTP server.

 *

 * @author Chris Ryan

 * @author Marcus Bointon <phpmailer@synchromedia.co.uk>

 */

class SMTP

{

    /**

     * The PHPMailer SMTP version number.

     *

     * @var string

     */

    const VERSION = '6.9.1';

    /**

     * SMTP line break constant.

     *

     * @var string

     */

    const LE = "\r\n";

    /**

     * The SMTP port to use if one is not specified.

     *

     * @var int

     */

    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.

     *

     * @see https://tools.ietf.org/html/rfc5321#section-4.5.3.1.6

     *

     * @var int

     */

    const MAX_LINE_LENGTH = 998;

    /**

     * The maximum line length allowed for replies in RFC 5321 section 4.5.3.1.5,

     * *including* a trailing CRLF line break.

     *

     * @see https://tools.ietf.org/html/rfc5321#section-4.5.3.1.5

     *

     * @var int

     */

    const MAX_REPLY_LENGTH = 512;

    /**

     * Debug level for no output.

     *

     * @var int

     */

    const DEBUG_OFF = 0;

    /**

     * Debug level to show client -> server messages.

     *

     * @var int

     */

    const DEBUG_CLIENT = 1;

    /**

     * Debug level to show client -> server and server -> client messages.

     *

     * @var int

     */

    const DEBUG_SERVER = 2;

    /**

     * Debug level to show connection status, client -> server and server -> client messages.

     *

     * @var int

     */

    const DEBUG_CONNECTION = 3;

    /**

     * Debug level to show all messages.

     *

     * @var int

     */

    const DEBUG_LOWLEVEL = 4;

    /**

     * Debug output level.

     * Options:

     * * self::DEBUG_OFF (`0`) No debug output, default

     * * self::DEBUG_CLIENT (`1`) Client commands

     * * 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.

     *

     * @var int

     */

    public $do_debug = self::DEBUG_OFF;

    /**

     * How to handle debug output.

     * Options:

     * * `echo` Output plain-text as-is, appropriate for CLI

     * * `html` Output escaped, line breaks converted to `<br>`, appropriate for browser output

     * * `error_log` Output to error log as configured in php.ini

     * Alternatively, you can provide a callable expecting two params: a message string and the debug level:

     *

     * ```php

     * $smtp->Debugoutput = function($str, $level) {echo "debug level $level; message: $str";};

     * ```

     *

     * Alternatively, you can pass in an instance of a PSR-3 compatible logger, though only `debug`

     * level output is used:

     *

     * ```php

     * $mail->Debugoutput = new myPsr3Logger;

     * ```

     *

     * @var string|callable|\Psr\Log\LoggerInterface

     */

    public $Debugoutput = 'echo';

    /**

     * Whether to use VERP.

     *

     * @see http://en.wikipedia.org/wiki/Variable_envelope_return_path

     * @see http://www.postfix.org/VERP_README.html Info on VERP

     *

     * @var bool

     */

    public $do_verp = false;

    /**

     * The timeout value for connection, in seconds.

     * 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.

     *

     * @see http://tools.ietf.org/html/rfc2821#section-4.5.3.2

     *

     * @var int

     */

    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.

     *

     * @var int

     */

    public $Timelimit = 300;

    /**

     * Patterns to extract an SMTP transaction id from reply to a DATA command.

     * The first capture group in each regex will be used as the ID.

     * MS ESMTP returns the message ID, which may not be correct for internal tracking.

     *

     * @var string[]

     */

    protected $smtp_transaction_id_patterns = [

        'exim' => '/[\d]{3} OK id=(.*)/',

        'sendmail' => '/[\d]{3} 2.0.0 (.*) Message/',

        'postfix' => '/[\d]{3} 2.0.0 Ok: queued as (.*)/',

        'Microsoft_ESMTP' => '/[0-9]{3} 2.[\d].0 (.*)@(?:.*) Queued mail for delivery/',

        '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 (.*)/',

    ];

    /**

     * Allowed SMTP XCLIENT attributes.

     * Must be allowed by the SMTP server. EHLO response is not checked.

     *

     * @see https://www.postfix.org/XCLIENT_README.html

     *

     * @var array

     */

    public static $xclient_allowed_attributes = [

        'NAME', 'ADDR', 'PORT', 'PROTO', 'HELO', 'LOGIN', 'DESTADDR', 'DESTPORT'

    ];

    /**

     * The last transaction ID issued in response to a DATA command,

     * if one was detected.

     *

     * @var string|bool|null

     */

    protected $last_smtp_transaction_id;

    /**

     * The socket for the server connection.

     *

     * @var ?resource

     */

    protected $smtp_conn;

    /**

     * Error information, if any, for the last SMTP command.

     *

     * @var array

     */

    protected $error = [

        'error' => '',

        'detail' => '',

        'smtp_code' => '',

        'smtp_code_ex' => '',

    ];

    /**

     * The reply the server sent to us for HELO.

     * If null, no HELO string has yet been received.

     *

     * @var string|null

     */

    protected $helo_rply;

    /**

     * The set of SMTP extensions sent in reply to EHLO command.

     * Indexes of the array are extension names.

     * Value at index 'HELO' or 'EHLO' (according to command that was sent)

     * 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.

     *

     * @var array|null

     */

    protected $server_caps;

    /**

     * The most recent reply received from the server.

     *

     * @var string

     */

    protected $last_reply = '';

    /**

     * Output debugging info via a user-selected method.

     *

     * @param string $str   Debug string to output

     * @param int    $level The debug level of this message; see DEBUG_* constants

     *

     * @see SMTP::$Debugoutput

     * @see SMTP::$do_debug

     */

    protected function edebug($str, $level = 0)

    {

        if ($level > $this->do_debug) {

            return;

        }

        //Is this a PSR-3 logger?

        if ($this->Debugoutput instanceof \Psr\Log\LoggerInterface) {

            $this->Debugoutput->debug($str);

            return;

        }

        //Avoid clash with built-in function names

        if (is_callable($this->Debugoutput) && !in_array($this->Debugoutput, ['error_log', 'html', 'echo'])) {

            call_user_func($this->Debugoutput, $str, $level);

            return;

        }

        switch ($this->Debugoutput) {

            case 'error_log':

                //Don't output, just log

                error_log($str);

                break;

            case 'html':

                //Cleans up output a bit for a better looking, HTML-safe output

                echo gmdate('Y-m-d H:i:s'), ' ', htmlentities(

                    preg_replace('/[\r\n]+/', '', $str),

                    ENT_QUOTES,

                    'UTF-8'

                ), "<br>\n";

                break;

            case 'echo':

            default:

                //Normalize line breaks

                $str = preg_replace('/\r\n|\r/m', "\n", $str);

                echo gmdate('Y-m-d H:i:s'),

                "\t",

                    //Trim trailing space

                trim(

                    //Indent for readability, except for trailing break

                    str_replace(

                        "\n",

                        "\n                   \t                  ",

                        trim($str)

                    )

                ),

                "\n";

        }

    }

    /**

     * Connect to an 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 bool

     */

    public function connect($host, $port = null, $timeout = 30, $options = [])

    {

        //Clear errors to avoid confusion

        $this->setError('');

        //Make sure we are __not__ connected

        if ($this->connected()) {

            //Already connected, generate error

            $this->setError('Already connected to a server');

            return false;

        }

        if (empty($port)) {

            $port = self::DEFAULT_PORT;

        }

        //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']);

            $connection = stream_socket_client(

                $host . ':' . $port,

                $errno,

                $errstr,

                $timeout,

                STREAM_CLIENT_CONNECT,

                $socket_context

            );

        } 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([$this, 'errorHandler']);

            $connection = fsockopen(

                $host,

                $port,

                $errno,

                $errstr,

                $timeout

            );

        }

        restore_error_handler();

        //Verify we connected properly

        if (!is_resource($connection)) {

            $this->setError(

                'Failed to connect to server',

                '',

                (string) $errno,

                $errstr

            );

            $this->edebug(

                'SMTP ERROR: ' . $this->error['error']

                . ": $errstr ($errno)",

                self::DEBUG_CLIENT

            );

            return false;

        }

        //SMTP server can take longer to respond, give longer timeout for first read

        //Windows does not have support for this timeout function

        if (strpos(PHP_OS, 'WIN') !== 0) {

            $max = (int)ini_get('max_execution_time');

            //Don't bother if unlimited, or if set_time_limit is disabled

            if (0 !== $max && $timeout > $max && strpos(ini_get('disable_functions'), 'set_time_limit') === false) {

                @set_time_limit($timeout);

            }

            stream_set_timeout($connection, $timeout, 0);

        }

        return $connection;

    }

    /**

     * Initiate a TLS (encrypted) session.

     *

     * @return bool

     */

    public function startTLS()

    {

        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

        set_error_handler([$this, 'errorHandler']);

        $crypto_ok = stream_socket_enable_crypto(

            $this->smtp_conn,

            true,

            $crypto_method

        );

        restore_error_handler();

        return (bool) $crypto_ok;

    }

    /**

     * 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 (CRAM-MD5, PLAIN, LOGIN, XOAUTH2)

     * @param OAuthTokenProvider $OAuth An optional OAuthTokenProvider instance for XOAUTH2 authentication

     *

     * @return bool True if successfully authenticated

     */

    public function authenticate(

        $username,

        $password,

        $authtype = null,

        $OAuth = null

    ) {

        if (!$this->server_caps) {

            $this->setError('Authentication is not allowed before HELO/EHLO');

            return false;

        }

        if (array_key_exists('EHLO', $this->server_caps)) {

            //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

                //e.g. after STARTTLS

                return false;

            }

            $this->edebug('Auth method requested: ' . ($authtype ?: 'UNSPECIFIED'), self::DEBUG_LOWLEVEL);

            $this->edebug(

                'Auth methods available on the server: ' . implode(',', $this->server_caps['AUTH']),

                self::DEBUG_LOWLEVEL

            );

            //If we have requested a specific auth type, check the server supports it before trying others

            if (null !== $authtype && !in_array($authtype, $this->server_caps['AUTH'], true)) {

                $this->edebug('Requested auth method not available: ' . $authtype, self::DEBUG_LOWLEVEL);

                $authtype = null;

            }

            if (empty($authtype)) {

                //If no auth mechanism is specified, attempt to use these, in this order

                //Try CRAM-MD5 first as it's more secure than the others

                foreach (['CRAM-MD5', 'LOGIN', 'PLAIN', 'XOAUTH2'] as $method) {

                    if (in_array($method, $this->server_caps['AUTH'], true)) {

                        $authtype = $method;

                        break;

                    }

                }

                if (empty($authtype)) {

                    $this->setError('No supported authentication methods found');

                    return false;

                }

                $this->edebug('Auth method selected: ' . $authtype, self::DEBUG_LOWLEVEL);

            }

            if (!in_array($authtype, $this->server_caps['AUTH'], true)) {

                $this->setError("The requested authentication method \"$authtype\" is not supported by the server");

                return false;

            }

        } elseif (empty($authtype)) {

            $authtype = 'LOGIN';

        }

        switch ($authtype) {

            case 'PLAIN':

                //Start authentication

                if (!$this->sendCommand('AUTH', 'AUTH PLAIN', 334)) {

                    return false;

                }

                //Send encoded username and password

                if (

                    //Format from https://tools.ietf.org/html/rfc4616#section-2

                    //We skip the first field (it's forgery), so the string starts with a null byte

                    !$this->sendCommand(

                        'User & Password',

                        base64_encode("\0" . $username . "\0" . $password),

                        235

                    )

                ) {

                    return false;

                }

                break;

            case 'LOGIN':

                //Start authentication

                if (!$this->sendCommand('AUTH', 'AUTH LOGIN', 334)) {

                    return false;

                }

                if (!$this->sendCommand('Username', base64_encode($username), 334)) {

                    return false;

                }

                if (!$this->sendCommand('Password', base64_encode($password), 235)) {

                    return false;

                }

                break;

            case 'CRAM-MD5':

                //Start authentication

                if (!$this->sendCommand('AUTH CRAM-MD5', 'AUTH CRAM-MD5', 334)) {

                    return false;

                }

                //Get the challenge

                $challenge = base64_decode(substr($this->last_reply, 4));

                //Build the response

                $response = $username . ' ' . $this->hmac($challenge, $password);

                //send encoded credentials

                return $this->sendCommand('Username', base64_encode($response), 235);

            case 'XOAUTH2':

                //The OAuth instance must be set up prior to requesting auth.

                if (null === $OAuth) {

                    return false;

                }

                $oauth = $OAuth->getOauth64();

                //Start authentication

                if (!$this->sendCommand('AUTH', 'AUTH XOAUTH2 ' . $oauth, 235)) {

                    return false;

                }

                break;

            default:

                $this->setError("Authentication method \"$authtype\" is not supported");

                return false;

        }

        return true;

    }

    /**

     * Calculate an MD5 HMAC hash.

     * Works like hash_hmac('md5', $data, $key)

     * in case that function is not available.

     *

     * @param string $data The data to hash

     * @param string $key  The key to hash with

     *

     * @return string

     */

    protected function hmac($data, $key)

    {

        if (function_exists('hash_hmac')) {

            return hash_hmac('md5', $data, $key);

        }

        //The following borrowed from

        //http://php.net/manual/en/function.mhash.php#27225

        //RFC 2104 HMAC implementation for php.

        //Creates an md5 HMAC.

        //Eliminates the need to install mhash to compute a HMAC

        //by Lance Rushing

        $bytelen = 64; //byte length for md5

        if (strlen($key) > $bytelen) {

            $key = pack('H*', md5($key));

        }

        $key = str_pad($key, $bytelen, chr(0x00));

        $ipad = str_pad('', $bytelen, chr(0x36));

        $opad = str_pad('', $bytelen, chr(0x5c));

        $k_ipad = $key ^ $ipad;

        $k_opad = $key ^ $opad;

        return md5($k_opad . pack('H*', md5($k_ipad . $data)));

    }

    /**

     * Check connection state.

     *

     * @return bool True if connected

     */

    public function connected()

    {

        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

                $this->edebug(

                    'SMTP NOTICE: EOF caught while checking if connected',

                    self::DEBUG_CLIENT

                );

                $this->close();

                return false;

            }

            return true; //everything looks good

        }

        return false;

    }

    /**

     * Close the socket and clean up the state of the class.

     * Don't use this function without first trying to use QUIT.

     *

     * @see quit()

     */

    public function close()

    {

        $this->server_caps = null;

        $this->helo_rply = null;

        if (is_resource($this->smtp_conn)) {

            //Close the connection and cleanup

            fclose($this->smtp_conn);

            $this->smtp_conn = null; //Makes for cleaner serialization

            $this->edebug('Connection: closed', self::DEBUG_CONNECTION);

        }

    }

    /**

     * Send an SMTP DATA command.

     * Issues a data command and sends the msg_data to the server,

     * finalizing the mail transaction. $msg_data is the message

     * that is to be sent 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>.

     * Implements RFC 821: DATA <CRLF>.

     *

     * @param string $msg_data Message data to send

     *

     * @return bool

     */

    public function data($msg_data)

    {

        //This will use the standard timelimit

        if (!$this->sendCommand('DATA', 'DATA', 354)) {

            return false;

        }

        /* The server is ready to accept data!

         * According to rfc821 we should not send more than 1000 characters on a single line (including the LE)

         * so we will break the data up into lines by \r and/or \n then if needed we will break each of those into

         * smaller lines to fit within the limit.

         * We will also look for lines that start with a '.' and prepend an additional '.'.

         * NOTE: this does not count towards line-length limit.

         */

        //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

         * of the first line (':' separated) does not contain a space then it _should_ be a header, and we will

         * process all lines before a blank line as headers.

         */

        $field = substr($lines[0], 0, strpos($lines[0], ':'));

        $in_headers = false;

        if (!empty($field) && strpos($field, ' ') === false) {

            $in_headers = true;

        }

        foreach ($lines as $line) {

            $lines_out = [];

            if ($in_headers && $line === '') {

                $in_headers = false;

            }

            //Break this line up into several smaller lines if it's too long

            //Micro-optimisation: isset($str[$len]) is faster than (strlen($str) > $len),

            while (isset($line[self::MAX_LINE_LENGTH])) {

                //Working backwards, try to find a space within the last MAX_LINE_LENGTH chars of the line to break on

                //so as to avoid breaking in the middle of a word

                $pos = strrpos(substr($line, 0, self::MAX_LINE_LENGTH), ' ');

                //Deliberately matches both false and 0

                if (!$pos) {

                    //No nice break found, add a hard break

                    $pos = self::MAX_LINE_LENGTH - 1;

                    $lines_out[] = substr($line, 0, $pos);

                    $line = substr($line, $pos);

                } else {

                    //Break at the found point

                    $lines_out[] = substr($line, 0, $pos);

                    //Move along by the amount we dealt with

                    $line = substr($line, $pos + 1);

                }

                //If processing headers add a LWSP-char to the front of new line RFC822 section 3.1.1

                if ($in_headers) {

                    $line = "\t" . $line;

                }

            }

            $lines_out[] = $line;

            //Send the lines to the server

            foreach ($lines_out as $line_out) {

                //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;

                }

                $this->client_send($line_out . static::LE, 'DATA');

            }

        }

        //Message data has been sent, complete the command

        //Increase timelimit for end of DATA command

        $savetimelimit = $this->Timelimit;

        $this->Timelimit *= 2;

        $result = $this->sendCommand('DATA END', '.', 250);

        $this->recordLastTransactionID();

        //Restore timelimit

        $this->Timelimit = $savetimelimit;

        return $result;

    }

    /**

     * Send an SMTP HELO or EHLO command.

     * Used to identify the sending server to the receiving server.

     * This makes sure that client and server are in a known state.

     * Implements RFC 821: HELO <SP> <domain> <CRLF>

     * and RFC 2821 EHLO.

     *

     * @param string $host The host name or IP to connect to

     *

     * @return bool

     */

    public function hello($host = '')

    {

        //Try extended hello first (RFC 2821)

        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);

    }

    /**

     * Send an SMTP HELO or EHLO command.

     * Low-level implementation used by hello().

     *

     * @param string $hello The HELO string

     * @param string $host  The hostname to say we are

     *

     * @return bool

     *

     * @see hello()

     */

    protected function sendHello($hello, $host)

    {

        $noerror = $this->sendCommand($hello, $hello . ' ' . $host, 250);

        $this->helo_rply = $this->last_reply;

        if ($noerror) {

            $this->parseHelloFields($hello);

        } else {

            $this->server_caps = null;

        }

        return $noerror;

    }

    /**

     * Parse a reply to HELO/EHLO command to discover server extensions.

     * In case of HELO, the only parameter that can be discovered is a server name.

     *

     * @param string $type `HELO` or `EHLO`

     */

    protected function parseHelloFields($type)

    {

        $this->server_caps = [];

        $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 (empty($s)) {

                continue;

            }

            $fields = explode(' ', $s);

            if (!empty($fields)) {

                if (!$n) {

                    $name = $type;

                    $fields = $fields[0];

                } else {

                    $name = array_shift($fields);

                    switch ($name) {

                        case 'SIZE':

                            $fields = ($fields ? $fields[0] : 0);

                            break;

                        case 'AUTH':

                            if (!is_array($fields)) {

                                $fields = [];

                            }

                            break;

                        default:

                            $fields = true;

                    }

                }

                $this->server_caps[$name] = $fields;

            }

        }

    }

    /**

     * Send an SMTP MAIL command.

     * Starts a mail transaction from the email address specified in

     * $from. Returns true if successful or false otherwise. If True

     * the mail transaction is started and then one or more recipient

     * commands may be called followed by a data command.

     * Implements RFC 821: MAIL <SP> FROM:<reverse-path> <CRLF>.

     *

     * @param string $from Source address of this message

     *

     * @return bool

     */

    public function mail($from)

    {

        $useVerp = ($this->do_verp ? ' XVERP' : '');

        return $this->sendCommand(

            'MAIL FROM',

            'MAIL FROM:<' . $from . '>' . $useVerp,

            250

        );

    }

    /**

     * Send an SMTP QUIT command.

     * Closes the socket if there is no error or the $close_on_error argument is true.

     * Implements from RFC 821: QUIT <CRLF>.

     *

     * @param bool $close_on_error Should the connection close if an error occurs?

     *

     * @return bool

     */

    public function quit($close_on_error = true)

    {

        $noerror = $this->sendCommand('QUIT', 'QUIT', 221);

        $err = $this->error; //Save any error

        if ($noerror || $close_on_error) {

            $this->close();

            $this->error = $err; //Restore any error from the quit command

        }

        return $noerror;

    }

    /**

     * Send an SMTP RCPT command.

     * 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 $address The address the message is being sent to

     * @param string $dsn     Comma separated list of DSN notifications. NEVER, SUCCESS, FAILURE

     *                        or DELAY. If you specify NEVER all other notifications are ignored.

     *

     * @return bool

     */

    public function recipient($address, $dsn = '')

    {

        if (empty($dsn)) {

            $rcpt = 'RCPT TO:<' . $address . '>';

        } else {

            $dsn = strtoupper($dsn);

            $notify = [];

            if (strpos($dsn, 'NEVER') !== false) {

                $notify[] = 'NEVER';

            } else {

                foreach (['SUCCESS', 'FAILURE', 'DELAY'] as $value) {

                    if (strpos($dsn, $value) !== false) {

                        $notify[] = $value;

                    }

                }

            }

            $rcpt = 'RCPT TO:<' . $address . '> NOTIFY=' . implode(',', $notify);

        }

        return $this->sendCommand(

            'RCPT TO',

            $rcpt,

            [250, 251]

        );

    }

    /**

     * Send SMTP XCLIENT command to server and check its return code.

     *

     * @return bool True on success

     */

    public function xclient(array $vars)

    {

        $xclient_options = "";

        foreach ($vars as $key => $value) {

            if (in_array($key, SMTP::$xclient_allowed_attributes)) {

                $xclient_options .= " {$key}={$value}";

            }

        }

        if (!$xclient_options) {

            return true;