<?php
/* vim: set expandtab softtabstop=4 tabstop=4 shiftwidth=4: */
// +----------------------------------------------------------------------+
// | PHP Version 4                                                        |
// +----------------------------------------------------------------------+
// | Copyright (c) 1997-2003 The PHP Group                                |
// +----------------------------------------------------------------------+
// | This source file is subject to version 2.02 of the PHP license,      |
// | that is bundled with this package in the file LICENSE, and is        |
// | available at through the world-wide-web at                           |
// | http://www.php.net/license/2_02.txt.                                 |
// | If you did not receive a copy of the PHP license and are unable to   |
// | obtain it through the world-wide-web, please send a note to          |
// | license@php.net so we can mail you a copy immediately.               |
// +----------------------------------------------------------------------+
// | Authors: Chuck Hagenbuch <chuck@horde.org>                           |
// |          Jon Parise <jon@php.net>                                    |
// |          Damian Alejandro Fernandez Sosa <damlists@cnba.uba.ar>      |
// +----------------------------------------------------------------------+
//
// $Id$

require_once 'PEAR.php';
require_once 'Net/Socket.php';

/**
 * Provides an implementation of the SMTP protocol using PEAR's
 * Net_Socket:: class.
 *
 * @package Net_SMTP
 * @author  Chuck Hagenbuch <chuck@horde.org>
 * @author  Jon Parise <jon@php.net>
 * @author  Damian Alejandro Fernandez Sosa <damlists@cnba.uba.ar>
 *
 * @example basic.php   A basic implementation of the Net_SMTP package.
 */
class Net_SMTP
{
    /**
     * The server to connect to.
     * @var string
     * @access public
     */
    var $host = 'localhost';

    /**
     * The port to connect to.
     * @var int
     * @access public
     */
    var $port = 25;

    /**
     * The value to give when sending EHLO or HELO.
     * @var string
     * @access public
     */
    var $localhost = 'localhost';

    /**
     * List of supported authentication methods, in preferential order.
     * @var array
     * @access public
     */
    var $auth_methods = array('DIGEST-MD5', 'CRAM-MD5', 'LOGIN', 'PLAIN');

    /**
     * Should debugging output be enabled?
     * @var boolean
     * @access private
     */
    var $_debug = false;

    /**
     * The socket resource being used to connect to the SMTP server.
     * @var resource
     * @access private
     */
    var $_socket = null;

    /**
     * The most recent server response code.
     * @var int
     * @access private
     */
    var $_code = -1;

    /**
     * The most recent server response arguments.
     * @var array
     * @access private
     */
    var $_arguments = array();

    /**
     * Stores detected features of the SMTP server.
     * @var array
     * @access private
     */
    var $_esmtp = array();

    /**
     * Instantiates a new Net_SMTP object, overriding any defaults
     * with parameters that are passed in.
     *
     * If you have SSL support in PHP, you can connect to a server
     * over SSL using an 'ssl://' prefix:
     *
     *   // 465 is a common smtps port.
     *   $smtp = new Net_SMTP('ssl://mail.host.com', 465);
     *   $smtp->connect();
     *
     * @param string  $host       The server to connect to.
     * @param integer $port       The port to connect to.
     * @param string  $localhost  The value to give when sending EHLO or HELO.
     *
     * @access  public
     * @since   1.0
     */
    function Net_SMTP($host = null, $port = null, $localhost = null)
    {
        if (isset($host)) $this->host = $host;
        if (isset($port)) $this->port = $port;
        if (isset($localhost)) $this->localhost = $localhost;

        $this->_socket = &new Net_Socket();

        /*
         * Include the Auth_SASL package.  If the package is not available,
         * we disable the authentication methods that depend upon it.
         */
        if ((@include_once 'Auth/SASL.php') === false) {
            $pos = array_search('DIGEST-MD5', $this->auth_methods);
            unset($this->auth_methods[$pos]);
            $pos = array_search('CRAM-MD5', $this->auth_methods);
            unset($this->auth_methods[$pos]);
        }
    }

    /**
     * Set the value of the debugging flag.
     *
     * @param   boolean $debug      New value for the debugging flag.
     *
     * @access  public
     * @since   1.1.0
     */
    function setDebug($debug)
    {
        $this->_debug = $debug;
    }

    /**
     * Send the given string of data to the server.
     *
     * @param   string  $data       The string of data to send.
     *
     * @return  mixed   True on success or a PEAR_Error object on failure.
     *
     * @access  private
     * @since   1.1.0
     */
    function _send($data)
    {
        if ($this->_debug) {
            echo "DEBUG: Send: $data\n";
        }

        if (PEAR::isError($error = $this->_socket->write($data))) {
            return PEAR::raiseError('Failed to write to socket: ' .
                                    $error->getMessage());
        }

        return true;
    }

    /**
     * Send a command to the server with an optional string of
     * arguments.  A carriage return / linefeed (CRLF) sequence will
     * be appended to each command string before it is sent to the
     * SMTP server - an error will be thrown if the command string
     * already contains any newline characters. Use _send() for
     * commands that must contain newlines.
     *
     * @param   string  $command    The SMTP command to send to the server.
     * @param   string  $args       A string of optional arguments to append
     *                              to the command.
     *
     * @return  mixed   The result of the _send() call.
     *
     * @access  private
     * @since   1.1.0
     */
    function _put($command, $args = '')
    {
        if (!empty($args)) {
            $command .= ' ' . $args;
        }

        if (strcspn($command, "\r\n") !== strlen($command)) {
            return PEAR::raiseError('Commands cannot contain newlines');
        }

        return $this->_send($command . "\r\n");
    }

    /**
     * Read a reply from the SMTP server.  The reply consists of a response
     * code and a response message.
     *
     * @param   mixed   $valid      The set of valid response codes.  These
     *                              may be specified as an array of integer
     *                              values or as a single integer value.
     *
     * @return  mixed   True if the server returned a valid response code or
     *                  a PEAR_Error object is an error condition is reached.
     *
     * @access  private
     * @since   1.1.0
     *
     * @see     getResponse
     */
    function _parseResponse($valid)
    {
        $this->_code = -1;
        $this->_arguments = array();

        while ($line = $this->_socket->readLine()) {
            if ($this->_debug) {
                echo "DEBUG: Recv: $line\n";
            }

            /* If we receive an empty line, the connection has been closed. */
            if (empty($line)) {
                $this->disconnect();
                return PEAR::raiseError('Connection was unexpectedly closed');
            }

            /* Read the code and store the rest in the arguments array. */
            $code = substr($line, 0, 3);
            $this->_arguments[] = trim(substr($line, 4));

            /* Check the syntax of the response code. */
            if (is_numeric($code)) {
                $this->_code = (int)$code;
            } else {
                $this->_code = -1;
                break;
            }

            /* If this is not a multiline response, we're done. */
            if (substr($line, 3, 1) != '-') {
                break;
            }
        }

        /* Compare the server's response code with the valid code. */
        if (is_int($valid) && ($this->_code === $valid)) {
            return true;
        }

        /* If we were given an array of valid response codes, check each one. */
        if (is_array($valid)) {
            foreach ($valid as $valid_code) {
                if ($this->_code === $valid_code) {
                    return true;
                }
            }
        }

        return PEAR::raiseError('Invalid response code received from server');
    }

    /**
     * Return a 2-tuple containing the last response from the SMTP server.
     *
     * @return  array   A two-element array: the first element contains the
     *                  response code as an integer and the second element
     *                  contains the response's arguments as a string.
     *
     * @access  public
     * @since   1.1.0
     */
    function getResponse()
    {
        return array($this->_code, join("\n", $this->_arguments));
    }

    /**
     * Attempt to connect to the SMTP server.
     *
     * @param   int     $timeout    The timeout value (in seconds) for the
     *                              socket connection.
     * @param   bool    $persistent Should a persistent socket connection
     *                              be used?
     *
     * @return mixed Returns a PEAR_Error with an error message on any
     *               kind of failure, or true on success.
     * @access public
     * @since  1.0
     */
    function connect($timeout = null, $persistent = false)
    {
        $result = $this->_socket->connect($this->host, $this->port,
                                          $persistent, $timeout);
        if (PEAR::isError($result)) {
            return PEAR::raiseError('Failed to connect socket: ' .
                                    $result->getMessage());
        }

        if (PEAR::isError($error = $this->_parseResponse(220))) {
            return $error;
        }
        if (PEAR::isError($error = $this->_negotiate())) {
            return $error;
        }

        return true;
    }

    /**
     * Attempt to disconnect from the SMTP server.
     *
     * @return mixed Returns a PEAR_Error with an error message on any
     *               kind of failure, or true on success.
     * @access public
     * @since  1.0
     */
    function disconnect()
    {
        if (PEAR::isError($error = $this->_put('QUIT'))) {
            return $error;
        }
        if (PEAR::isError($error = $this->_parseResponse(221))) {
            return $error;
        }
        if (PEAR::isError($error = $this->_socket->disconnect())) {
            return PEAR::raiseError('Failed to disconnect socket: ' .
                                    $error->getMessage());
        }

        return true;
    }

    /**
     * Attempt to send the EHLO command and obtain a list of ESMTP
     * extensions available, and failing that just send HELO.
     *
     * @return mixed Returns a PEAR_Error with an error message on any
     *               kind of failure, or true on success.
     *
     * @access private
     * @since  1.1.0
     */
    function _negotiate()
    {
        if (PEAR::isError($error = $this->_put('EHLO', $this->localhost))) {
            return $error;
        }

        if (PEAR::isError($this->_parseResponse(250))) {
            /* If we receive a 503 response, we're already authenticated. */
            if ($this->_code === 503) {
                return true;
            }

            /* If the EHLO failed, try the simpler HELO command. */
            if (PEAR::isError($error = $this->_put('HELO', $this->localhost))) {
                return $error;
            }
            if (PEAR::isError($this->_parseResponse(250))) {
                return PEAR::raiseError('HELO was not accepted: ', $this->_code);
            }

            return true;
        }

        foreach ($this->_arguments as $argument) {
            $verb = strtok($argument, ' ');
            $arguments = substr($argument, strlen($verb) + 1,
                                strlen($argument) - strlen($verb) - 1);
            $this->_esmtp[$verb] = $arguments;
        }

        return true;
    }

    /**
     * Returns the name of the best authentication method that the server
     * has advertised.
     *
     * @return mixed    Returns a string containing the name of the best
     *                  supported authentication method or a PEAR_Error object
     *                  if a failure condition is encountered.
     * @access private
     * @since  1.1.0
     */
    function _getBestAuthMethod()
    {
        $available_methods = explode(' ', $this->_esmtp['AUTH']);

        foreach ($this->auth_methods as $method) {
            if (in_array($method, $available_methods)) {
                return $method;
            }
        }

        return PEAR::raiseError('No supported authentication methods');
    }

    /**
     * Attempt to do SMTP authentication.
     *
     * @param string The userid to authenticate as.
     * @param string The password to authenticate with.
     * @param string The requested authentication method.  If none is
     *               specified, the best supported method will be used.
     *
     * @return mixed Returns a PEAR_Error with an error message on any
     *               kind of failure, or true on success.
     * @access public
     * @since  1.0
     */
    function auth($uid, $pwd , $method = '')
    {
        if (empty($this->_esmtp['AUTH'])) {
            return PEAR::raiseError('SMTP server does no support authentication');
        }

        /* If no method has been specified, get the name of the best
         * supported method advertised by the SMTP server. */
        if (empty($method)) {
            if (PEAR::isError($method = $this->_getBestAuthMethod())) {
                /* Return the PEAR_Error object from _getBestAuthMethod(). */
                return $method;
            }
        } else {
            $method = strtoupper($method);
            if (!in_array($method, $this->auth_methods)) {
                return PEAR::raiseError("$method is not a supported authentication method");
            }
        }

        switch ($method) {
            case 'DIGEST-MD5':
                $result = $this->_authDigest_MD5($uid, $pwd);
                break;
            case 'CRAM-MD5':
                $result = $this->_authCRAM_MD5($uid, $pwd);
                break;
            case 'LOGIN':
                $result = $this->_authLogin($uid, $pwd);
                break;
            case 'PLAIN':
                $result = $this->_authPlain($uid, $pwd);
                break;
            default:
                $result = PEAR::raiseError("$method is not a supported authentication method");
                break;
        }

        /* If an error was encountered, return the PEAR_Error object. */
        if (PEAR::isError($result)) {
            return $result;
        }

        return true;
    }

    /**
     * Authenticates the user using the DIGEST-MD5 method.
     *
     * @param string The userid to authenticate as.
     * @param string The password to authenticate with.
     *
     * @return mixed Returns a PEAR_Error with an error message on any
     *               kind of failure, or true on success.
     * @access private
     * @since  1.1.0
     */
    function _authDigest_MD5($uid, $pwd)
    {
        if (PEAR::isError($error = $this->_put('AUTH', 'DIGEST-MD5'))) {
            return $error;
        }
        /* 334: Continue authentication request */
        if (PEAR::isError($error = $this->_parseResponse(334))) {
            /* 503: Error: already authenticated */
            if ($this->_code === 503) {
                return true;
            }
            return $error;
        }

        $challenge = base64_decode($this->_arguments[0]);
        $digest = &Auth_SASL::factory('digestmd5');
        $auth_str = base64_encode($digest->getResponse($uid, $pwd, $challenge,
                                                       $this->host, "smtp"));

        if (PEAR::isError($error = $this->_put($auth_str))) {
            return $error;
        }
        /* 334: Continue authentication request */
        if (PEAR::isError($error = $this->_parseResponse(334))) {
            return $error;
        }

        /* We don't use the protocol's third step because SMTP doesn't
         * allow subsequent authentication, so we just silently ignore
         * it. */
        if (PEAR::isError($error = $this->_put(' '))) {
            return $error;
        }
        /* 235: Authentication successful */
        if (PEAR::isError($error = $this->_parseResponse(235))) {
            return $error;
        }
    }

    /**
     * Authenticates the user using the CRAM-MD5 method.
     *
     * @param string The userid to authenticate as.
     * @param string The password to authenticate with.
     *
     * @return mixed Returns a PEAR_Error with an error message on any
     *               kind of failure, or true on success.
     * @access private
     * @since  1.1.0
     */
    function _authCRAM_MD5($uid, $pwd)
    {
        if (PEAR::isError($error = $this->_put('AUTH', 'CRAM-MD5'))) {
            return $error;
        }
        /* 334: Continue authentication request */
        if (PEAR::isError($error = $this->_parseResponse(334))) {
            /* 503: Error: already authenticated */
            if ($this->_code === 503) {
                return true;
            }
            return $error;
        }

        $challenge = base64_decode($this->_arguments[0]);
        $cram = &Auth_SASL::factory('crammd5');
        $auth_str = base64_encode($cram->getResponse($uid, $pwd, $challenge));

        if (PEAR::isError($error = $this->_put($auth_str))) {
            return $error;
        }

        /* 235: Authentication successful */
        if (PEAR::isError($error = $this->_parseResponse(235))) {
            return $error;
        }
    }

    /**
     * Authenticates the user using the LOGIN method.
     *
     * @param string The userid to authenticate as.
     * @param string The password to authenticate with.
     *
     * @return mixed Returns a PEAR_Error with an error message on any
     *               kind of failure, or true on success.
     * @access private
     * @since  1.1.0
     */
    function _authLogin($uid, $pwd)
    {
        if (PEAR::isError($error = $this->_put('AUTH', 'LOGIN'))) {
            return $error;
        }
        /* 334: Continue authentication request */
        if (PEAR::isError($error = $this->_parseResponse(334))) {
            /* 503: Error: already authenticated */
            if ($this->_code === 503) {
                return true;
            }
            return $error;
        }

        if (PEAR::isError($error = $this->_put(base64_encode($uid)))) {
            return $error;
        }
        /* 334: Continue authentication request */
        if (PEAR::isError($error = $this->_parseResponse(334))) {
            return $error;
        }

        if (PEAR::isError($error = $this->_put(base64_encode($pwd)))) {
            return $error;
        }

        /* 235: Authentication successful */
        if (PEAR::isError($error = $this->_parseResponse(235))) {
            return $error;
        }

        return true;
    }

    /**
     * Authenticates the user using the PLAIN method.
     *
     * @param string The userid to authenticate as.
     * @param string The password to authenticate with.
     *
     * @return mixed Returns a PEAR_Error with an error message on any
     *               kind of failure, or true on success.
     * @access private
     * @since  1.1.0
     */
    function _authPlain($uid, $pwd)
    {
        if (PEAR::isError($error = $this->_put('AUTH', 'PLAIN'))) {
            return $error;
        }
        /* 334: Continue authentication request */
        if (PEAR::isError($error = $this->_parseResponse(334))) {
            /* 503: Error: already authenticated */
            if ($this->_code === 503) {
                return true;
            }
            return $error;
        }

        $auth_str = base64_encode(chr(0) . $uid . chr(0) . $pwd);

        if (PEAR::isError($error = $this->_put($auth_str))) {
            return $error;
        }

        /* 235: Authentication successful */
        if (PEAR::isError($error = $this->_parseResponse(235))) {
            return $error;
        }

        return true;
    }

    /**
     * Send the HELO command.
     *
     * @param string The domain name to say we are.
     *
     * @return mixed Returns a PEAR_Error with an error message on any
     *               kind of failure, or true on success.
     * @access public
     * @since  1.0
     */
    function helo($domain)
    {
        if (PEAR::isError($error = $this->_put('HELO', $domain))) {
            return $error;
        }
        if (PEAR::isError($error = $this->_parseResponse(250))) {
            return $error;
        }

        return true;
    }

    /**
     * Send the MAIL FROM: command.
     *
     * @param string $sender    The sender (reverse path) to set.
     * @param string $params    String containing additional MAIL parameters,
     *                          such as the NOTIFY flags defined by RFC 1891
     *                          or the VERP protocol.
     *
     *                          If $params is an array, only the 'verp' option
     *                          is supported.  If 'verp' is true, the XVERP
     *                          parameter is appended to the MAIL command.  If
     *                          the 'verp' value is a string, the full
     *                          XVERP=value parameter is appended.
     *
     * @return mixed Returns a PEAR_Error with an error message on any
     *               kind of failure, or true on success.
     * @access public
     * @since  1.0
     */
    function mailFrom($sender, $params = null)
    {
        $args = "FROM:<$sender>";

        /* Support the deprecated array form of $params. */
        if (is_array($params) && isset($params['verp'])) {
            /* XVERP */
            if ($params['verp'] === true) {
                $args .= ' XVERP';

            /* XVERP=something */
            } elseif (trim($params['verp'])) {
                $args .= ' XVERP=' . $params['verp'];
            }
        } elseif (is_string($params)) {
            $args .= ' ' . $params;
        }

        if (PEAR::isError($error = $this->_put('MAIL', $args))) {
            return $error;
        }
        if (PEAR::isError($error = $this->_parseResponse(250))) {
            return $error;
        }

        return true;
    }

    /**
     * Send the RCPT TO: command.
     *
     * @param string $recipient The recipient (forward path) to add.
     * @param string $params    String containing additional RCPT parameters,
     *                          such as the NOTIFY flags defined by RFC 1891.
     *
     * @return mixed Returns a PEAR_Error with an error message on any
     *               kind of failure, or true on success.
     *
     * @access public
     * @since  1.0
     */
    function rcptTo($recipient, $params = null)
    {
        $args = "TO:<$recipient>";
        if (is_string($params)) {
            $args .= ' ' . $params;
        }

        if (PEAR::isError($error = $this->_put('RCPT', $args))) {
            return $error;
        }
        if (PEAR::isError($error = $this->_parseResponse(array(250, 251)))) {
            return $error;
        }

        return true;
    }

    /**
     * Quote the data so that it meets SMTP standards.
     *
     * This is provided as a separate public function to facilitate
     * easier overloading for the cases where it is desirable to
     * customize the quoting behavior.
     *
     * @param string $data  The message text to quote. The string must be passed
     *                      by reference, and the text will be modified in place.
     *
     * @access public
     * @since  1.2
     */
    function quotedata(&$data)
    {
        /* Change Unix (\n) and Mac (\r) linefeeds into
         * Internet-standard CRLF (\r\n) linefeeds. */
        $data = preg_replace(array('/(?<!\r)\n/','/\r(?!\n)/'), "\r\n", $data);

        /* Because a single leading period (.) signifies an end to the
         * data, legitimate leading periods need to be "doubled"
         * (e.g. '..'). */
        $data = str_replace("\n.", "\n..", $data);
    }

    /**
     * Send the DATA command.
     *
     * @param string $data  The message body to send.
     *
     * @return mixed Returns a PEAR_Error with an error message on any
     *               kind of failure, or true on success.
     * @access public
     * @since  1.0
     */
    function data($data)
    {
        /* RFC 1870, section 3, subsection 3 states "a value of zero
         * indicates that no fixed maximum message size is in force".
         * Furthermore, it says that if "the parameter is omitted no
         * information is conveyed about the server's fixed maximum
         * message size". */
        if (isset($this->_esmtp['SIZE']) && ($this->_esmtp['SIZE'] > 0)) {
            if (strlen($data) >= $this->_esmtp['SIZE']) {
                $this->disconnect();
                return PEAR::raiseError('Message size excedes the server limit');
            }
        }

        /* Quote the data based on the SMTP standards. */
        $this->quotedata($data);

        if (PEAR::isError($error = $this->_put('DATA'))) {
            return $error;
        }
        if (PEAR::isError($error = $this->_parseResponse(354))) {
            return $error;
        }

        if (PEAR::isError($result = $this->_send($data . "\r\n.\r\n"))) {
            return $result;
        }
        if (PEAR::isError($error = $this->_parseResponse(250))) {
            return $error;
        }

        return true;
    }

    /**
     * Send the SEND FROM: command.
     *
     * @param string The reverse path to send.
     *
     * @return mixed Returns a PEAR_Error with an error message on any
     *               kind of failure, or true on success.
     * @access public
     * @since  1.2.6
     */
    function sendFrom($path)
    {
        if (PEAR::isError($error = $this->_put('SEND', "FROM:<$path>"))) {
            return $error;
        }
        if (PEAR::isError($error = $this->_parseResponse(250))) {
            return $error;
        }

        return true;
    }

    /**
     * Backwards-compatibility wrapper for sendFrom().
     *
     * @param string The reverse path to send.
     *
     * @return mixed Returns a PEAR_Error with an error message on any
     *               kind of failure, or true on success.
     *
     * @access      public
     * @since       1.0
     * @deprecated  1.2.6
     */
    function send_from($path)
    {
        return sendFrom($path);
    }

    /**
     * Send the SOML FROM: command.
     *
     * @param string The reverse path to send.
     *
     * @return mixed Returns a PEAR_Error with an error message on any
     *               kind of failure, or true on success.
     * @access public
     * @since  1.2.6
     */
    function somlFrom($path)
    {
        if (PEAR::isError($error = $this->_put('SOML', "FROM:<$path>"))) {
            return $error;
        }
        if (PEAR::isError($error = $this->_parseResponse(250))) {
            return $error;
        }

        return true;
    }

    /**
     * Backwards-compatibility wrapper for somlFrom().
     *
     * @param string The reverse path to send.
     *
     * @return mixed Returns a PEAR_Error with an error message on any
     *               kind of failure, or true on success.
     *
     * @access      public
     * @since       1.0
     * @deprecated  1.2.6
     */
    function soml_from($path)
    {
        return somlFrom($path);
    }

    /**
     * Send the SAML FROM: command.
     *
     * @param string The reverse path to send.
     *
     * @return mixed Returns a PEAR_Error with an error message on any
     *               kind of failure, or true on success.
     * @access public
     * @since  1.2.6
     */
    function samlFrom($path)
    {
        if (PEAR::isError($error = $this->_put('SAML', "FROM:<$path>"))) {
            return $error;
        }
        if (PEAR::isError($error = $this->_parseResponse(250))) {
            return $error;
        }

        return true;
    }

    /**
     * Backwards-compatibility wrapper for samlFrom().
     *
     * @param string The reverse path to send.
     *
     * @return mixed Returns a PEAR_Error with an error message on any
     *               kind of failure, or true on success.
     *
     * @access      public
     * @since       1.0
     * @deprecated  1.2.6
     */
    function saml_from($path)
    {
        return samlFrom($path);
    }

    /**
     * Send the RSET command.
     *
     * @return mixed Returns a PEAR_Error with an error message on any
     *               kind of failure, or true on success.
     * @access public
     * @since  1.0
     */
    function rset()
    {
        if (PEAR::isError($error = $this->_put('RSET'))) {
            return $error;
        }
        if (PEAR::isError($error = $this->_parseResponse(250))) {
            return $error;
        }

        return true;
    }

    /**
     * Send the VRFY command.
     *
     * @param string The string to verify
     *
     * @return mixed Returns a PEAR_Error with an error message on any
     *               kind of failure, or true on success.
     * @access public
     * @since  1.0
     */
    function vrfy($string)
    {
        /* Note: 251 is also a valid response code */
        if (PEAR::isError($error = $this->_put('VRFY', $string))) {
            return $error;
        }
        if (PEAR::isError($error = $this->_parseResponse(array(250, 252)))) {
            return $error;
        }

        return true;
    }

    /**
     * Send the NOOP command.
     *
     * @return mixed Returns a PEAR_Error with an error message on any
     *               kind of failure, or true on success.
     * @access public
     * @since  1.0
     */
    function noop()
    {
        if (PEAR::isError($error = $this->_put('NOOP'))) {
            return $error;
        }
        if (PEAR::isError($error = $this->_parseResponse(250))) {
            return $error;
        }

        return true;
    }

    /**
     * Backwards-compatibility method.  identifySender()'s functionality is
     * now handled internally.
     *
     * @return  boolean     This method always return true.
     *
     * @access  public
     * @since   1.0
     */
    function identifySender()
    {
        return true;
    }

}