//namespace to use 
System.Text.RegularExpressions
//use this function for checking email is valid or not
public bool Emailcheck(string Email)
        {
            Regex regex;
            regex = new Regex(@"\S+@\S+\.\S+");
            if (regex.IsMatch(Email))
            {
                return true;
            }
            else
            {
                return false;
            }
        }