using System;
using System.Text.RegularExpressions;

public class Test
{
	public static void Main()
	{
		string email = "an.email@ahost.com";
		string regex = @"^([\w-\.]+)@((\[[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.)|(([\w-]+\.)+))([a-zA-Z]{2,4}|[0-9]{1,3})(\]?)$";
		
		Regex rgx = new Regex(regex);
		
		Boolean result = rgx.IsMatch(email);
		System.Console.WriteLine("{0} validation is {1}", email, result.ToString());
	}
}