$email = "test@ansoncheung.com";  if (preg_match('/^[^0-9][a-zA-Z0-9_]+([.][a-zA-Z0-9_]+)*[@][a-zA-Z0-9_]+([.][a-zA-Z0-9_]+)*[.][a-zA-Z]{2,4}$/',$email)) {      echo "Your email is ok.";  } else {      echo "Wrong email address format";  }