using System;

using System.Text.RegularExpressions;

public class Program

{

    public static void Main()

    {

        var email = "rob@son@totvs.com.br";

      Regex regexEmail = new Regex(@"^([\w\.\-]+)@([\w\-]+)((\.(\w){2,3})+)$");

      System.Text.RegularExpressions.Match match = regexEmail.Match(email);     

      if(match.Success)

        Console.WriteLine("Sucesso");

      else

        Console.WriteLine("Erro");            

    }

}