Check valid Email Address in PHP code

function validate_email($email)
{

  // Create the syntactical validation regular expression
  $regexp = "^([_a-z0-9-]+)(\.[_a-z0-9-]+)*@([a-z0-9-]+)(\.[a-z0-9-]+)*(\.[a-z]{2,4})$";

  // Presume that the email is invalid
  $valid = 0;

  // Validate the syntax
  if (eregi($regexp, $email))
  {
     list($username,$domaintld) = split("@",$email);
     // Validate the domain
     if (getmxrr($domaintld,$mxrecords))
        $valid = 1;
  } else {
     $valid = 0;
  }

  return $valid;

}