Email validation problem REGEX on IE7

public static bool emailid(string em)
       {
           const string MatchEmailPattern =
             @"^(([\w-]+\.)+[\w-]+|([a-zA-Z]{1}|[\w-]{2,}))@"
      + @"((([0-1]?[0-9]{1,2}|25[0-5]|2[0-4][0-9])\.([0-1]?
               [0-9]{1,2}|25[0-5]|2[0-4][0-9])\."
      + @"([0-1]?[0-9]{1,2}|25[0-5]|2[0-4][0-9])\.([0-1]?
               [0-9]{1,2}|25[0-5]|2[0-4][0-9])){1}|"
      + @"([a-zA-Z]+[\w-]+\.)+[a-zA-Z]{2,4})$";



           if (!Regex.IsMatch(em, MatchEmailPattern))
               return true;
           else
               return false;

       }

}@(?=[a-zA-Z0-9-\.]{0,255}\.?\s*$)[