code for validating email in c#.net

You can have a look on MailAddress Class[^]

public bool IsValid(string emailaddress)
{
    try
    {
        MailAddress m = new MailAddress(emailaddress);
        return true;
    }
    catch (FormatException)
    {
        return false;
    }
}

This is something where you don't need to understand any other's regx code.

Also have a look on this example where you can get an example with source for email validation
c# regex for email address[^]

An alternative:

public bool IsValidEmailAddress(string s)
        {
            if (string.IsNullOrEmpty(s))
                return false;
            else
            {
                var regex = new Regex(@"\w+([-+.']\w+)*@\w+([-.]\w+)*\.\w+([-.]\w+)*");
                return regex.IsMatch(s) && !s.EndsWith(".");
            }
        }