c# - returns true boolean if valid email address, not case sensitive

gistfile1.txt

public bool checkIfEmail(string checkString){
			
		
			string regex=@"^(?("")(""[^""]+?""@)|(([0-9a-z]((\.(?!\.))|[-!#\$%&'\*\+/=\?\^`\{\}\|~\w])*)(?<=[0-9a-z])@))" + 
                @"(?(\[)(\[(\d{1,3}\.){3}\d{1,3}\])|(([0-9a-z][-\w]*[0-9a-z]*\.)+[a-z0-9]{2,24}))$";
		
			return Regex.IsMatch(checkString,regex,RegexOptions.IgnoreCase);
			
		}