<?php
function isEmail($email, $check_mx = true) {
    // all characters except @ and whitespace
    $name = '[^@\s]+';

    // letters, numbers, hyphens separated by a period
    $sub_domain = '[-a-z0-9]+\.';

    // country codes
    $cc = '[a-z]{2}';

    // top level domains
    $tlds = "$cc|com|net|edu|org|gov|mil|int|biz|pro|info|arpa|aero|coop|name|museum";

    $email_pattern = "/^$name@($sub_domain)+($tlds)$/ix";

    if (preg_match($email_pattern, $email, $check_pieces)) {
        // check mail exchange or DNS
        if ($check_mx) {
            $host = substr(strstr($check_pieces[0], '@'), 1);
            if (in_array($host, $skip_check)) {
                return true;
            }

            //Check DNS records
            if(checkdnsrr($host, "MX")) {
                if(!getmxrr($host, $mxhost, $mxweight)) {
                    return false;
                }
            } else {
                $mxhost[] = $host;
                $mxweight[] = 1;
            }

            $weighted_host = array();
            for($i = 0; $i < count($mxhost); $i ++) {
                $weighted_host[($mxweight[$i])] = $mxhost[$i];
            }
            ksort($weighted_host);

            foreach($weighted_host as $host) {
                if (!($fp = @fsockopen($host, 25, $errno, $errstr))) {
                    continue;
                }

                $stopTime = time() + 12;
                $gotResponse = FALSE;
                stream_set_blocking($fp, FALSE);

                while(true) {
                    $strresp = fgets($fp, 1024);
                    if(substr($strresp, 0, 3) == "220") {
                        $stopTime = time() + 12;
                        $gotResponse = true;
                    } elseif (($strresp == "") && ($gotResponse)) {
                        break;
                    } elseif(time() > $stopTime) {
                        break;
                    }
                }
                if(!$gotResponse) {
                    continue;
                }
                stream_set_blocking($fp, true);

                fputs($fp, "HELO {$_SERVER['SERVER_NAME']}\r\n");
                fgets($fp, 1024);

                fputs($fp, "MAIL FROM: <httpd@{$_SERVER['SERVER_NAME']}>\r\n");
                fgets($fp, 1024);

                fputs($fp, "RCPT TO: <$email>\r\n");
                $line = fgets($fp, 1024);

                fputs($fp, "QUIT\r\n");

                fclose($fp);
                if(substr($line, 0, 3) != "250") {
                    return false;
                } else {
                    return true;
                }
            }
            return false;
        }
        return true;
    }
    return false;
}
?>