Email_verification.php

$email = 'test@domain.com';

if(verify_email($email)){

    // E-mail address looks to be in the proper format
    // lets check the MX records

    if(verify_email_dns($email)){

        // E-mail passed both checks
        echo 'Success - E-mail address appears to be valid.';

    } else {

        // E-mail is invalid, no MC record
        echo 'Error - E-mail domain does not have an MX record.';

    }

} else {

    // E-mail inst formatted correctly
    // so we dont even check its MX record
    echo 'Error - E-mail address appears to be invalid.';

}

// Our function to filter our bogus formatted addresses
function verify_email($email){

    if(!preg_match('/^[_A-z0-9-]+((\.|\+)[_A-z0-9-]+)*@[A-z0-9-]+(\.[A-z0-9-]+)*(\.[A-z]{2,4})$/',$email)){
        return false;
    } else {
        return $email;
    }
}

// Our function to verify the MX records
function verify_email_dns($email){

    // This will split the email into its front
    // and back (the domain) portions
    list($name, $domain) = split('@',$email);

    if(!checkdnsrr($domain,'MX')){

        // No MX record found
        return false;

    } else {

        // MX record found, return email
        return $email;

    }
}