root/cemail/include/validate_email.php

<?php
/*
    File : verifyemail_lib.php
    Version : 1.1
    Date :  November 20th, 2002
    Author : Lars B. Jensen, lars.jensen@ljweb.com

    Module Description
    Module to verify if email is valid in three different levels.
    Level 1 : Correct formatting of email
    Level 2 : Server exists in DNS as MX record
    Level 3 : Does the user exist on the email given
    
    !!! Warning !!!
    Level 3 checking does take a considerable amount of time !!!


    Note
    Functions used in script is not implemented in windows versions of PHP !
    
    SMTP Reference
    http://www.ietf.org/rfc/rfc0821.txt?number=821
    

    Public Functions
    --------------------------------------------------------------
    function verifyemail_validateemail($email)
    function verifyemail_validatehost($email, $return_mxhost=0)
    function verifyemail_validateexists($email)

    Private Functions
    --------------------------------------------------------------
    function verifyemail_closesocket($socket)
    function verifyemail_localhost()
*/

    function verifyemail_validateemail($email) {
        if (!preg_match("/^([\w|\.|\-|_]+)@([\w||\-|_]+)\.([\w|\.|\-|_]+)$/i", $email)) {
            return false;
            exit;
        }
    
        return true;
    }


    function verifyemail_validatehost($email, $return_mxhost=0) {
        if (!verifyemail_validateemail($email)) {
            return false;
            exit;
        }
    
        list($local,$domain) = explode("@",$email,2);
        
        $mxhosts = array();
        if(!checkdnsrr($domain, "MX") || !getmxrr($domain, $mxhosts)) {
            return false;
            exit;
        }

        if ($return_mxhost) {
            return $mxhosts;
            exit;
        }
        
        return true;
    }


    function verifyemail_validateexists($email) {
        $mxhosts = verifyemail_validatehost($email, true);
        
        if (!is_array($mxhosts)) {
            return false;
            exit;
        }

        $found = false;
        $localhost = verifyemail_localhost();

        $mxsize = sizeof($mxhosts);
        for($i=0; $i<$mxsize; $i++)    {
            $socket = fsockopen($mxhosts[$i], 25);

            if(!$socket) continue;

            $foo = fgets($socket, 4096);

            # 220 <domain> Service ready
            if(!preg_match("/^220/i", $foo)) { 
                verifyemail_closesocket($socket);
                continue;
            }

            fputs($socket, "HELO ".$localhost."\r\n");
            $foo = fgets($socket);
            while (preg_match("/^220/i", $foo)) {
                $foo = fgets($socket, 4096);
            }

            fputs($socket, "VRFY ".$email."\r\n");
            $foo = fgets($socket, 4096);

            # 250 Requested mail action okay, completed
            if(preg_match("/^250/i", $foo)) {
                $found = true;
                verifyemail_closesocket($socket);

                break;
            }

            # 550 Requested action not taken: mailbox unavailable [E.g., mailbox not found, no access]
            if(preg_match("/^550/i", $foo)) {
                verifyemail_closesocket($socket);
                continue;
            }

            fputs($socket, "MAIL FROM: <".$email.">\r\n");
            $foo = fgets($socket, 4096);

            fputs($socket, "RCPT TO: <".$email.">\r\n");
            $foo = fgets($socket, 4096);

            # 250 Requested mail action okay, completed
            # 251 User not local; will forward to <forward-path>
            if(preg_match("/^[250|251]/i", $foo)) {
                $found = true;
                verifyemail_closesocket($socket);

                break;
            }
        
            verifyemail_closesocket($socket);
        }

        return $found;
    }


    function verifyemail_closesocket($socket) {
        fputs($socket, "QUIT\r\n");
        fclose($socket);
        
        return true;
    }


    function verifyemail_localhost() {
        $localhost = getenv("SERVER_NAME");
        if (!strlen($localhost)) $localhost = getenv("HOST");

        return $localhost;
    }
?>