Try below code for Asp.Net(C#) Email Validation.
public static bool IsValidEmail(string email)
{
System.Text.RegularExpressions.Regex rx = new System.Text.RegularExpressions.Regex(@"^[-!#$%&'*+/0-9=?A-Z^_a-z{|}~](\.?[-!#$%&'*+/0-9=?A-Z^_a-z{|}~])*@[a-zA-Z](-?[a-zA-Z0-9])*(\.[a-zA-Z](-?[a-zA-Z0-9])*)+$");
return rx.IsMatch(email);
}