PHPMailer / PHPMailer

src/SMTP.php

<?php
/**
 * PHPMailer RFC821 SMTP email transport class.
 * PHP Version 5.5
 *
 * @package   PHPMailer
 * @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 - 2016 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.
 *
 * @package PHPMailer
 * @author  Chris Ryan
 * @author  Marcus Bointon <phpmailer@synchromedia.co.uk>
 */
class SMTP
{
    /**
     * The PHPMailer SMTP version number.
     *
     * @var string
     */
    const VERSION = '6.0.0';

    /**
     * SMTP line break constant.
     *
     * @var string
     */
    const LE = "\r\n";

    /**
     * The SMTP port to use if one is not specified.
     *
     * @var integer
     */
    const DEFAULT_PORT = 25;

    /**
     * The maximum line length allowed by RFC 2822 section 2.1.1
     *
     * @var integer
     */
    const MAX_LINE_LENGTH = 998;

    /**
     * Debug level for no output
     */
    const DEBUG_OFF = 0;

    /**
     * Debug level to show client -> server messages
     */
    const DEBUG_CLIENT = 1;

    /**
     * Debug level to show client -> server and server -> client messages
     */
    const DEBUG_SERVER = 2;

    /**
     * Debug level to show connection status, client -> server and server -> client messages
     */
    const DEBUG_CONNECTION = 3;

    /**
     * Debug level to show all messages
     */
    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 integer
     */
    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:
     * <code>
     * $smtp->Debugoutput = function($str, $level) {echo "debug level $level; message: $str";};
     * </code>
     * Alternatively, you can pass in an instance of a PSR-3 compatible logger, though only `debug`
     * level output is used:
     * <code>
     * $mail->Debugoutput = new myPsr3Logger;
     * </code>
     *
     * @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 boolean
     */
    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 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
     *
     * @var integer
     */
    public $Timelimit = 300;

    /**
     * @var array 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.
     */
    protected $smtp_transaction_id_patterns = [
        'exim' => '/[0-9]{3} OK id=(.*)/',
        'sendmail' => '/[0-9]{3} 2.0.0 (.*) Message/',
        'postfix' => '/[0-9]{3} 2.0.0 Ok: queued as (.*)/',
        'Microsoft_ESMTP' => '/[0-9]{3} 2.[0-9].0 (.*)@(?:.*) Queued mail for delivery/'
    ];

    /**
     * @var string The last transaction ID issued in response to a DATA command,
     * if one was detected
     */
    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 = null;

    /**
     * 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 = null;

    /**
     * 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 integer $level The debug level of this message; see DEBUG_* constants
     *
     * @see SMTP::$Debugoutput
     * @see SMTP::$do_debug
     */
    protected function edebug($str, $level = 0)
    {
        if ($level > $this->do_debug) {
            return;
        }
        //Is this a PSR-3 logger?
        if (is_a($this->Debugoutput, 'Psr\Log\LoggerInterface')) {
            $this->Debugoutput->debug($str);
            return;
        }
        //Avoid clash with built-in function names
        if (!in_array($this->Debugoutput, ['error_log', 'html', 'echo']) and is_callable($this->Debugoutput)) {
            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/ms', "\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 integer $port The port number to connect to
     * @param integer $timeout How long to wait for the connection to open
     * @param array $options An array of options for stream_context_create()
     *
     * @return boolean
     */
    public function connect($host, $port = null, $timeout = 30, $options = [])
    {
        static $streamok;
        //This is enabled by default since 5.0.0 but some providers disable it
        //Check this once and cache the result
        if (is_null($streamok)) {
            $streamok = function_exists('stream_socket_client');
        }
        // 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
        );
        $errno = 0;
        $errstr = '';
        if ($streamok) {
            $socket_context = stream_context_create($options);
            set_error_handler([$this, 'errorHandler']);
            $this->smtp_conn = stream_socket_client(
                $host . ":" . $port,
                $errno,
                $errstr,
                $timeout,
                STREAM_CLIENT_CONNECT,
                $socket_context
            );
            restore_error_handler();
        } else {
            //Fall back to fsockopen which should work in more places, but is missing some features
            $this->edebug(
                "Connection: stream_socket_client not available, falling back to fsockopen",
                self::DEBUG_CONNECTION
            );
            set_error_handler([$this, 'errorHandler']);
            $this->smtp_conn = fsockopen(
                $host,
                $port,
                $errno,
                $errstr,
                $timeout
            );
            restore_error_handler();
        }
        // Verify we connected properly
        if (!is_resource($this->smtp_conn)) {
            $this->setError(
                'Failed to connect to server',
                $errno,
                $errstr
            );
            $this->edebug(
                'SMTP ERROR: ' . $this->error['error']
                . ": $errstr ($errno)",
                self::DEBUG_CLIENT
            );
            return false;
        }
        $this->edebug('Connection: opened', self::DEBUG_CONNECTION);
        // SMTP server can take longer to respond, give longer timeout for first read
        // Windows does not have support for this timeout function
        if (substr(PHP_OS, 0, 3) != 'WIN') {
            $max = ini_get('max_execution_time');
            // Don't bother if unlimited
            if (0 != $max and $timeout > $max) {
                @set_time_limit($timeout);
            }
            stream_set_timeout($this->smtp_conn, $timeout, 0);
        }
        // Get any announcement
        $announce = $this->get_lines();
        $this->edebug('SERVER -> CLIENT: ' . $announce, self::DEBUG_SERVER);
        return true;
    }

    /**
     * Initiate a TLS (encrypted) session.
     *
     * @return boolean
     */
    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,
            $crypto_method
        );
        restore_error_handler();
        return (boolean)$crypto_ok;
    }

    /**
     * Perform SMTP authentication.
     * Must be run after hello().
     *
     * @param string $username The user name
     * @param string $password The password
     * @param string $authtype The auth type (CRAM-MD5, PLAIN, LOGIN, XOAUTH2)
     * @param OAuth $OAuth An optional OAuth instance for XOAUTH2 authentication
     *
     * @return boolean True if successfully authenticated.
     * @see    hello()
     */
    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 ? $authtype : 'UNKNOWN'), 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 (!in_array($authtype, $this->server_caps['AUTH'])) {
                $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'])) {
                        $authtype = $method;
                        break;
                    }
                }
                if (empty($authtype)) {
                    $this->setError('No supported authentication methods found');
                    return false;
                }
                self::edebug('Auth method selected: ' . $authtype, self::DEBUG_LOWLEVEL);
            }

            if (!in_array($authtype, $this->server_caps['AUTH'])) {
                $this->setError("The requested authentication method \"$authtype\" is not supported by the server");
                return false;
            }
        } elseif (empty($authtype)) {
            $authtype = 'LOGIN';
        }
        switch ($authtype) {
            case 'PLAIN':
                // Start authentication
                if (!$this->sendCommand('AUTH', 'AUTH PLAIN', 334)) {
                    return false;
                }
                // Send encoded username and password
                if (!$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 (is_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 boolean 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->setError('');
        $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,
     * finializing the mail transaction. $msg_data is the message
     * that is to be send with the headers. Each header needs to be
     * on a single line followed by a <CRLF> with the message headers
     * and the message body being separated by an additional <CRLF>.
     * Implements RFC 821: DATA <CRLF>
     *
     * @param string $msg_data Message data to send
     *
     * @return boolean
     */
    public function data($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) and strpos($field, ' ') === false) {
            $in_headers = true;
        }

        foreach ($lines as $line) {
            $lines_out = [];
            if ($in_headers and $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 $line_out) {
                //RFC2821 section 4.5.2
                if (!empty($line_out) and $line_out[0] == '.') {
                    $line_out = '.' . $line_out;
                }
                $this->client_send($line_out . static::LE);
            }
        }

        //Message data has been sent, complete the command
        //Increase timelimit for end of DATA command
        $savetimelimit = $this->Timelimit;
        $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 $host The host name or IP to connect to
     *
     * @return boolean
     */
    public function hello($host = '')
    {
        //Try extended hello first (RFC 2821)
        return (boolean)($this->sendHello('EHLO', $host) or $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 $host The hostname to say we are
     *
     * @return boolean
     * @see    hello()
     */
    protected function sendHello($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 $from Source address of this message
     *
     * @return boolean
     */
    public function mail($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 boolean $close_on_error Should the connection close if an error occurs?
     *
     * @return boolean
     */
    public function quit($close_on_error = true)
    {
        $noerror = $this->sendCommand('QUIT', 'QUIT', 221);
        $err = $this->error; //Save any error
        if ($noerror or $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 $address The address the message is being sent to
     *
     * @return boolean
     */
    public function recipient($address)
    {
        return $this->sendCommand(
            'RCPT TO',
            'RCPT TO:<' . $address . '>',
            [250, 251]
        );
    }

    /**
     * Send an SMTP RSET command.
     * Abort any transaction that is currently in progress.
     * Implements RFC 821: RSET <CRLF>
     *
     * @return boolean True on success.
     */
    public function reset()
    {
        return $this->sendCommand('RSET', 'RSET', 250);
    }

    /**
     * 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 $commandstring The actual command to send
     * @param integer|array $expect One or more expected integer success codes
     *
     * @return boolean True on success.
     */
    protected function sendCommand($command, $commandstring, $expect)
    {
        if (!$this->connected()) {
            $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 . static::LE);

        $this->last_reply = $this->get_lines();
        // Fetch SMTP code and possible error code explanation
        $matches = [];
        if (preg_match("/^([0-9]{3})[ -](?:([0-9]\\.[0-9]\\.[0-9]) )?/", $this->last_reply, $matches)) {
            $code = $matches[1];
            $code_ex = (count($matches) > 2 ? $matches[2] : null);
            // Cut off error code from each response line
            $detail = preg_replace(
                "/{$code}[ -]" .
                ($code_ex ? str_replace('.', '\\.', $code_ex) . ' ' : '') . "/m",
                '',
                $this->last_reply
            );
        } else {
            // Fall back to simple parsing if regex fails
            $code = substr($this->last_reply, 0, 3);
            $code_ex = null;
            $detail = substr($this->last_reply, 4);
        }

        $this->edebug('SERVER -> CLIENT: ' . $this->last_reply, self::DEBUG_SERVER);

        if (!in_array($code, (array)$expect)) {
            $this->setError(
                "$command command failed",
                $detail,
                $code,
                $code_ex
            );
            $this->edebug(
                'SMTP ERROR: ' . $this->error['error'] . ': ' . $this->last_reply,
                self::DEBUG_CLIENT
            );
            return false;
        }

        $this->setError('');
        return true;
    }

    /**
     * Send an SMTP SAML 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. This command
     * will send the message to the users terminal if they are logged
     * in and send them an email.
     * Implements RFC 821: SAML <SP> FROM:<reverse-path> <CRLF>
     *
     * @param string $from The address the message is from
     *
     * @return boolean
     */
    public function sendAndMail($from)
    {
        return $this->sendCommand('SAML', "SAML FROM:$from", 250);
    }

    /**
     * Send an SMTP VRFY command.
     *
     * @param string $name The name to verify
     *
     * @return boolean
     */
    public function verify($name)
    {
        return $this->sendCommand('VRFY', "VRFY $name", [250, 251]);
    }

    /**
     * Send an SMTP NOOP command.
     * Used to keep keep-alives alive, doesn't actually do anything
     *
     * @return boolean
     */
    public function noop()
    {
        return $this->sendCommand('NOOP', 'NOOP', 250);
    }

    /**
     * Send an SMTP TURN command.
     * This is an optional command for SMTP that this class does not support.
     * This method is here to make the RFC821 Definition complete for this class
     * and _may_ be implemented in future
     * Implements from RFC 821: TURN <CRLF>
     *
     * @return boolean
     */
    public function turn()
    {
        $this->setError('The SMTP TURN command is not implemented');
        $this->edebug('SMTP NOTICE: ' . $this->error['error'], self::DEBUG_CLIENT);
        return false;
    }

    /**
     * Send raw data to the server.
     *
     * @param string $data The data to send
     *
     * @return integer|boolean The number of bytes sent to the server or false on error
     */
    public function client_send($data)
    {
        $this->edebug("CLIENT -> SERVER: $data", self::DEBUG_CLIENT);
        set_error_handler([$this, 'errorHandler']);
        $result = fwrite($this->smtp_conn, $data);
        restore_error_handler();
        return $result;
    }

    /**
     * Get the latest error.
     *
     * @return array
     */
    public function getError()
    {
        return $this->error;
    }

    /**
     * Get SMTP extensions available on the server
     *
     * @return array|null
     */
    public function getServerExtList()
    {
        return $this->server_caps;
    }

    /**
     * A multipurpose method
     * The method works in three ways, dependent on argument value and current state
     *   1. HELO/EHLO was not sent - returns null and set up $this->error
     *   2. HELO was sent
     *     $name = 'HELO': returns server name
     *     $name = 'EHLO': returns boolean false
     *     $name = any string: returns null and set up $this->error
     *   3. EHLO was sent
     *     $name = 'HELO'|'EHLO': returns server name
     *     $name = any string: if extension $name exists, returns boolean True
     *       or its options. Otherwise returns boolean False
     * In other words, one can use this method to detect 3 conditions:
     *  - null returned: handshake was not or we don't know about ext (refer to $this->error)
     *  - false returned: the requested feature exactly not exists
     *  - positive value returned: the requested feature exists
     *
     * @param string $name Name of SMTP extension or 'HELO'|'EHLO'
     *
     * @return mixed
     */
    public function getServerExt($name)
    {
        if (!$this->server_caps) {
            $this->setError('No HELO/EHLO was sent');
            return null;
        }

        // the tight logic knot ;)
        if (!array_key_exists($name, $this->server_caps)) {
            if ('HELO' == $name) {
                return $this->server_caps['EHLO'];
            }
            if ('EHLO' == $name || array_key_exists('EHLO', $this->server_caps)) {
                return false;
            }
            $this->setError('HELO handshake was used. Client knows nothing about server extensions');
            return null;
        }

        return $this->server_caps[$name];
    }

    /**
     * Get the last reply from the server.
     *
     * @return string
     */
    public function getLastReply()
    {
        return $this->last_reply;
    }

    /**
     * Read the SMTP server's response.
     * Either before eof or socket timeout occurs on the operation.
     * With SMTP we can tell if we have more lines to read if the
     * 4th character is '-' symbol. If it is a space then we don't
     * need to read anything else.
     *
     * @return string
     */
    protected function get_lines()
    {
        // If the connection is bad, give up straight away
        if (!is_resource($this->smtp_conn)) {
            return '';
        }
        $data = '';
        $endtime = 0;
        stream_set_timeout($this->smtp_conn, $this->Timeout);
        if ($this->Timelimit > 0) {
            $endtime = time() + $this->Timelimit;
        }
        $selR = [$this->smtp_conn];
        $selW = null;
        while (is_resource($this->smtp_conn) and !feof($this->smtp_conn)) {
            //Must pass vars in here as params are by reference
            if (!stream_select($selR, $selW, $selW, $this->Timelimit)) {
                $this->edebug(
                    'SMTP -> get_lines(): timed-out (' . $this->Timeout . ' sec)',
                    self::DEBUG_LOWLEVEL
                );
                break;
            }
            //Deliberate noise suppression - errors are handled afterwards
            $str = @fgets($this->smtp_conn, 515);
            $this->edebug("SMTP INBOUND: \"". trim($str).'"', self::DEBUG_LOWLEVEL);
            $data .= $str;
            // If response is only 3 chars (not valid, but RFC5321 S4.2 says it must be handled),
            // or 4th character is a space, we are done reading, break the loop,
            // string array access is a micro-optimisation over strlen
            if (!isset($str[3]) or (isset($str[3]) and $str[3] == ' ')) {
                break;
            }
            // Timed-out? Log and break
            $info = stream_get_meta_data($this->smtp_conn);
            if ($info['timed_out']) {
                $this->edebug(
                    'SMTP -> get_lines(): timed-out (' . $this->Timeout . ' sec)',
                    self::DEBUG_LOWLEVEL
                );
                break;
            }
            // Now check if reads took too long
            if ($endtime and time() > $endtime) {
                $this->edebug(
                    'SMTP -> get_lines(): timelimit reached (' .
                    $this->Timelimit . ' sec)',
                    self::DEBUG_LOWLEVEL
                );
                break;
            }
        }
        return $data;
    }

    /**
     * Enable or disable VERP address generation.
     *
     * @param boolean $enabled
     */
    public function setVerp($enabled = false)
    {
        $this->do_verp = $enabled;
    }

    /**
     * Get VERP address generation mode.
     *
     * @return boolean
     */
    public function getVerp()
    {
        return $this->do_verp;
    }

    /**
     * Set error messages and codes.
     *
     * @param string $message The error message
     * @param string $detail Further detail on the error
     * @param string $smtp_code An associated SMTP error code
     * @param string $smtp_code_ex Extended SMTP code
     */
    protected function setError($message, $detail = '', $smtp_code = '', $smtp_code_ex = '')
    {
        $this->error = [
            'error' => $message,
            'detail' => $detail,
            'smtp_code' => $smtp_code,
            'smtp_code_ex' => $smtp_code_ex
        ];
    }

    /**
     * Set debug output method.
     *
     * @param string|callable $method The name of the mechanism to use for debugging output, or a callable to handle it.
     */
    public function setDebugOutput($method = 'echo')
    {
        $this->Debugoutput = $method;
    }

    /**
     * Get debug output method.
     *
     * @return string
     */
    public function getDebugOutput()
    {
        return $this->Debugoutput;
    }

    /**
     * Set debug output level.
     *
     * @param integer $level
     */
    public function setDebugLevel($level = 0)
    {
        $this->do_debug = $level;
    }

    /**
     * Get debug output level.
     *
     * @return integer
     */
    public function getDebugLevel()
    {
        return $this->do_debug;
    }

    /**
     * Set SMTP timeout.
     *
     * @param integer $timeout
     */
    public function setTimeout($timeout = 0)
    {
        $this->Timeout = $timeout;
    }

    /**
     * Get SMTP timeout.
     *
     * @return integer
     */
    public function getTimeout()
    {
        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.
     * @param string $errfile The file the error occurred in
     * @param integer $errline The line number the error occurred on
     */
    protected function errorHandler($errno, $errmsg, $errfile = '', $errline = 0)
    {
        $notice = 'Connection failed.';
        $this->setError(
            $notice,
            $errno,
            $errmsg
        );
        $this->edebug(
            $notice . ' Error #' . $errno . ': ' . $errmsg . " [$errfile line $errline]",
            self::DEBUG_CONNECTION
        );
    }

    /**
     * Extract and return the ID of the last SMTP transaction based on
     * a list of patterns provided in SMTP::$smtp_transaction_id_patterns.
     * Relies on the host providing the ID in response to a DATA command.
     * If no reply has been received yet, it will return null.
     * If no pattern was matched, it will return false.
     * @return bool|null|string
     */
    protected function recordLastTransactionID()
    {
        $reply = $this->getLastReply();

        if (empty($reply)) {
            $this->last_smtp_transaction_id = null;
        } else {
            $this->last_smtp_transaction_id = false;

The property $last_smtp_transaction_id was declared of type string, but false is of type false. Maybe add a type cast?

            foreach ($this->smtp_transaction_id_patterns as $smtp_transaction_id_pattern) {
                if (preg_match($smtp_transaction_id_pattern, $reply, $matches)) {
                    $this->last_smtp_transaction_id = $matches[1];
                }
            }
        }

        return $this->last_smtp_transaction_id;
    }

    /**
     * Get the queue/transaction ID of the last SMTP transaction
     * If no reply has been received yet, it will return null.
     * If no pattern was matched, it will return false.
     * @return bool|null|string
     * @see recordLastTransactionID()
     */
    public function getLastTransactionID()
    {
        return $this->last_smtp_transaction_id;
    }
}