A PHP class file that can be used to check if an email address is valid using SMTP protocol. Visit https://www.davidangulo.xyz/ for more information.

class.verifyEmail.php

<?php

/**
 * Class to check up e-mail
 *
 * @author Konstantin Granin <[email protected]>
 * @copyright Copyright (c) 2015, Konstantin Granin
 */
class verifyEmail {

	protected $stream = false;

	/**
	 * SMTP port number
	 * @var int
	 */
	protected $port = 25;

	/**
	 * email address for request
	 * @var string 
	 */
	protected $from = '[email protected]';

	/**
	 * The connection timeout, in seconds.
	 * @var int
	 */
	protected $max_connection_timeout = 30;

	/**
	 * Timeout value on stream, in seconds.
	 * @var int
	 */
	protected $stream_timeout = 5;

	/**
	 * Wait timeout on stream, in seconds.
	 * * 0 - not wait
	 * @var int
	 */
	protected $stream_timeout_wait = 0;

	/**
	 * Whether to throw exceptions for errors.
	 * @type boolean
	 * @access protected
	 */
	protected $exceptions = false;

	/**
	 * The number of errors encountered.
	 * @type integer
	 * @access protected
	 */
	protected $error_count = 0;

	/**
	 * class debug output mode.
	 * @type boolean
	 */
	public $Debug = false;

	/**
	 * 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
	 * * `log` Output to error log as configured in php.ini
	 * @type string
	 */
	public $Debugoutput = 'echo';

	/**
	 * SMTP RFC standard line ending.
	 */
	const CRLF = "\r\n";

	/**
	 * Holds the most recent error message.
	 * @type string
	 */
	public $ErrorInfo = '';

	/**
	 * Constructor.
	 * @param boolean $exceptions Should we throw external exceptions?
	 */
	public function __construct($exceptions = false) {
		$this->exceptions = (boolean) $exceptions;
	}

	/**
	 * Set email address for SMTP request
	 * @param string $email Email address
	 */
	public function setEmailFrom($email) {
		if (!self::validate($email)) {
			$this->set_error('Invalid address : ' . $email);
			$this->edebug($this->ErrorInfo);
			if ($this->exceptions) {
				throw new verifyEmailException($this->ErrorInfo);
			}
		}
		$this->from = $email;
	}

	/**
	 * Set connection timeout, in seconds.
	 * @param int $seconds
	 */
	public function setConnectionTimeout($seconds) {
		if ($seconds > 0) {
			$this->max_connection_timeout = (int) $seconds;
		}
	}

	/**
	 * Sets the timeout value on stream, expressed in the seconds
	 * @param int $seconds
	 */
	public function setStreamTimeout($seconds) {
		if ($seconds > 0) {
			$this->stream_timeout = (int) $seconds;
		}
	}

	public function setStreamTimeoutWait($seconds) {
		if ($seconds >= 0) {
			$this->stream_timeout_wait = (int) $seconds;
		}
	}

	/**
	 * Validate email address.
	 * @param string $email
	 * @return boolean  True if valid.
	 */
	public static function validate($email) {
		return (boolean) filter_var($email, FILTER_VALIDATE_EMAIL);
	}

	/**
	 * Get array of MX records for host. Sort by weight information.
	 * @param string $hostname The Internet host name.
	 * @return array Array of the MX records found.
	 */
	public function getMXrecords($hostname) {
		$mxhosts = array();
		$mxweights = array();
		if (getmxrr($hostname, $mxhosts, $mxweights) === FALSE) {
			$this->set_error('MX records not found or an error occurred');
			$this->edebug($this->ErrorInfo);
		} else {
			array_multisort($mxweights, $mxhosts);
		}
		/**
		 * Add A-record as last chance (e.g. if no MX record is there).
		 * Thanks Nicht Lieb.
		 * @link http://www.faqs.org/rfcs/rfc2821.html RFC 2821 - Simple Mail Transfer Protocol
		 */
		if (empty($mxhosts)) {
			$mxhosts[] = $hostname;
		}
		return $mxhosts;
	}

	/**
	 * Parses input string to array(0=>user, 1=>domain)
	 * @param string $email
	 * @param boolean $only_domain
	 * @return string|array
	 * @access private
	 */
	public static function parse_email($email, $only_domain = TRUE) {
		sscanf($email, "%[^@]@%s", $user, $domain);
		return ($only_domain) ? $domain : array($user, $domain);
	}

	/**
	 * Add an error message to the error container.
	 * @access protected
	 * @param string $msg
	 * @return void
	 */
	protected function set_error($msg) {
		$this->error_count++;
		$this->ErrorInfo = $msg;
	}

	/**
	 * Check if an error occurred.
	 * @access public
	 * @return boolean True if an error did occur.
	 */
	public function isError() {
		return ($this->error_count > 0);
	}

	/**
	 * Output debugging info
	 * Only generates output if debug output is enabled
	 * @see verifyEmail::$Debugoutput
	 * @see verifyEmail::$Debug
	 * @param string $str
	 */
	protected function edebug($str) {
		if (!$this->Debug) {
			return;
		}
		switch ($this->Debugoutput) {
			case '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 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|\n)/ms', "\n", $str);
				echo gmdate('Y-m-d H:i:s') . "\t" . str_replace(
						"\n", "\n                   \t                  ", trim($str)
				) . "\n";
		}
	}

	/**
	 * check up e-mail
	 * @param string $email Email address
	 * @return boolean True if the valid email also exist
	 */
	public function check($email) {
		$result = FALSE;

		if (!self::validate($email)) {
			$this->set_error("{$email} incorrect e-mail");
			$this->edebug($this->ErrorInfo);
			if ($this->exceptions) {
				throw new verifyEmailException($this->ErrorInfo);
			}
			return FALSE;
		}
		$this->error_count = 0; // Reset errors
		$this->stream = FALSE;

		$mxs = $this->getMXrecords(self::parse_email($email));
		$timeout = ceil($this->max_connection_timeout / count($mxs));
		foreach ($mxs as $host) {
			/**
			 * suppress error output from stream socket client...
			 * Thanks Michael.
			 */
			$this->stream = @stream_socket_client("tcp://" . $host . ":" . $this->port, $errno, $errstr, $timeout);
			if ($this->stream === FALSE) {
				if ($errno == 0) {
					$this->set_error("Problem initializing the socket");
					$this->edebug($this->ErrorInfo);
					if ($this->exceptions) {
						throw new verifyEmailException($this->ErrorInfo);
					}
					return FALSE;
				} else {
					$this->edebug($host . ":" . $errstr);
				}
			} else {
				stream_set_timeout($this->stream, $this->stream_timeout);
				stream_set_blocking($this->stream, 1);

				if ($this->_streamCode($this->_streamResponse()) == '220') {
					$this->edebug("Connection success {$host}");
					break;
				} else {
					fclose($this->stream);
					$this->stream = FALSE;
				}
			}
		}

		if ($this->stream === FALSE) {
			$this->set_error("All connection fails");
			$this->edebug($this->ErrorInfo);
			if ($this->exceptions) {
				throw new verifyEmailException($this->ErrorInfo);
			}
			return FALSE;
		}

		$this->_streamQuery("HELO " . self::parse_email($this->from));
		$this->_streamResponse();
		$this->_streamQuery("MAIL FROM: <{$this->from}>");
		$this->_streamResponse();
		$this->_streamQuery("RCPT TO: <{$email}>");
		$code = $this->_streamCode($this->_streamResponse());
		//$this->_streamResponse();
		$this->_streamQuery("RSET");
		//$this->_streamResponse();
		$this->_streamQuery("QUIT");

		fclose($this->stream);

		switch ($code) {
			case '250':
			/**
			 * http://www.ietf.org/rfc/rfc0821.txt
			 * 250 Requested mail action okay, completed
			 * email address was accepted
			 */
			case '450':
			case '451':
			case '452':
				/**
				 * http://www.ietf.org/rfc/rfc0821.txt
				 * 450 Requested action not taken: the remote mail server
				 *     does not want to accept mail from your server for
				 *     some reason (IP address, blacklisting, etc..)
				 *     Thanks Nicht Lieb.
				 * 451 Requested action aborted: local error in processing
				 * 452 Requested action not taken: insufficient system storage
				 * email address was greylisted (or some temporary error occured on the MTA)
				 * i believe that e-mail exists
				 */
				return TRUE;
			default :
				return FALSE;
		}
	}

	/**
	 * writes the contents of string to the file stream pointed to by handle 
	 * If an error occurs, returns FALSE.
	 * @access protected
	 * @param string $string The string that is to be written
	 * @return string Returns a result code, as an integer. 
	 */
	protected function _streamQuery($query) {
		$this->edebug($query);
		return stream_socket_sendto($this->stream, $query . self::CRLF);
	}

	/**
	 * Reads all the line long the answer and analyze it.
	 * If an error occurs, returns FALSE
	 * @access protected
	 * @return string Response
	 */
	protected function _streamResponse($timed = 0) {
		$reply = stream_get_line($this->stream, 1);
		$status = stream_get_meta_data($this->stream);

		if (!empty($status['timed_out'])) {
			$this->edebug("Timed out while waiting for data! (timeout {$this->stream_timeout} seconds)");
		}

		if ($reply === FALSE && $status['timed_out'] && $timed < $this->stream_timeout_wait) {
			return $this->_streamResponse($timed + $this->stream_timeout);
		}


		if ($reply !== FALSE && $status['unread_bytes'] > 0) {
			$reply .= stream_get_line($this->stream, $status['unread_bytes'], self::CRLF);
		}
		$this->edebug($reply);
		return $reply;
	}

	/**
	 * Get Response code from Response
	 * @param string $str
	 * @return string
	 */
	protected function _streamCode($str) {
		preg_match('/^(?<code>[0-9]{3})(\s|-)(.*)$/ims', $str, $matches);
		$code = isset($matches['code']) ? $matches['code'] : false;
		return $code;
	}

}

/**
 * verifyEmail exception handler
 */
class verifyEmailException extends Exception {

	/**
	 * Prettify error message output
	 * @return string
	 */
	public function errorMessage() {
		//$errorMsg = '<strong>' . $this->getMessage() . "</strong><br />\n";
		$errorMsg = $this->getMessage();
		return $errorMsg;
	}

}

?>

example-complete.php

<html>
	<head>
		<title>Sample</title>
	</head>
	<body>
		<?php
		include_once 'class.verifyEmail.php';
        	if(isset($_GET["email"])) {
			$email = $_GET["email"];
			$vmail = new verifyEmail();
			$vmail->setStreamTimeoutWait(20);
			$vmail->Debug= TRUE;
			$vmail->Debugoutput= 'html';
			$vmail->setEmailFrom('[email protected]'); //change this email address
			if ($vmail->check($email)) {
				echo 'email ' . $email . ' exist!';
			} 
			elseif (verifyEmail::validate($email)) {
				echo 'email ' . $email . ' valid, but not exist!';
			} 
			else {
				echo 'email ' . $email . ' not valid and not exist!';
			}
          	}
		?>
		<form action="" method="get">
			<input type="email" name="email">
			<button type="submit">Submit</button>
		</form>
    </body>
</html>

example-form.php

<html>
	<head>
		<title>Sample</title>
	</head>
	<body>
		<form action="" method="get">
			<input type="email" name="email">
			<button type="submit">Submit</button>
		</form>
	</body>
</html>