PHP regular verification email function

 function isemail($email) {
 return strlen($email) > 8 && preg_match("/^[-_+.[:alnum:]]+@((([ [:alnum:]]|[[:alnum:]][[:alnum:]-]*[[:alnum:]]).)+([a-z]{2,4})|(([0- 9][0-9]?|[0-1][0-9][0-9]|[2][0-4][0-9]|[2][5][0-5] ).){3}([0-9][0-9]?|[0-1][0-9][0-9]|[2][0-4][0-9]|[ 2][5][0-5]))$/i", $email);
 }
 if(!isemail($_POST['email'])) {
 echo "Sorry, the verification email address is incorrect! ";
 exit();
 }
?>