php 邮箱验证函数

function checkEmail($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; }