using System;

using System.Text.RegularExpressions;               

public class Program

{

    public static void Main()

    {

        var EmailId1="test@gmail.com";

        var EmailId2= "test1212@com";

        string pattern = @"\A(?:[a-z0-9!#$%&'*+/=?^_`{|}~-]+(?:\.[a-z0-9!#$%&'*+/=?^_`{|}~-]+)*@(?:[a-z0-9](?:[a-z0-9-]*[a-z0-9])?\.)+[a-z0-9](?:[a-z0-9-]*[a-z0-9])?)\Z";

        //check first string

       if (Regex.IsMatch(EmailId1 , pattern))

       {    

           //if email is valid

            Console.WriteLine(EmailId1+ " is a valid Email address ");

       }

       else

       {

            Console.WriteLine(EmailId1 + " is not a valid Email address");          

       }

​

        //check second string

       if (Regex.IsMatch(EmailId2 , pattern))

       {         

           //print if email id is valid

            Console.WriteLine(EmailId2+ " is Valid Email address ");

       }

       else

       {

           //print if email id is not valid

            Console.WriteLine(EmailId2 + " is Not a Valid Email address");          

       }

    }

}