using System;

using System.Text.RegularExpressions;

​

public class Program

{

    public static void Main()

    {

        string[] emailsToValidate = new string[] {'a@b'};

        Regex regex = new Regex(@"^(?=.{1,254}$)(?=.{1,64}@)[-!#$%&'*+/0-9=?A-Z^_`a-z{|}~]+(\.[-!#$%&'*+/0-9=?A-Z^_`a-z{|}~]+)*@[A-Za-z0-9]([A-Za-z0-9-]{0,61}[A-Za-z0-9])?(\.[A-Za-z0-9]([A-Za-z0-9-]{0,61}[A-Za-z0-9])?)*$");

        Match match = regex.Match(emailToValidate);

        foreach (var emailToValidate in emailsToValidate)

            Console.WriteLine("{0}: {1}", match.Success, match.Value);

    }

}