using System;

​

public class Program

{

    public static void Main()

    {

        while (true)

        {

            Console.WriteLine("Enter an email address to validate.");

            string input = Console.ReadLine();

            if (input == "stop")

                return;

            try

            {

                System.Net.Mail.MailAddress emailAddr = new System.Net.Mail.MailAddress(input);

                if (!emailAddr.Host.Contains("."))

                    throw new Exception("Email host address must contain a period.");

                Console.WriteLine("\"" + input + "\" is valid!");

            }

            catch (Exception ex) 

            {

                Console.WriteLine("INVALID - \"" + input + "\". Error: "+ ex.Message);

            }

        }

    }

}