email regex

Email regular expression, with domain name validation.

function checkEmail($email) {
 if(preg_match("^([a-zA-Z0-9])+([a-zA-Z0-9\._-])*@([a-zA-Z0-9_-])+([a-zA-Z0-9\._-]+)+$",$email))
 {
    list($username,$domain)=split('@',$email);
    if(!checkdnsrr($domain,'MX')) {
        return false;
      }
 return true;
 }
 return false;
}