Some SMTP servers require that the client be authenticated before the server sends e-mail on its behalf. In this case, you can include the EmailUseDefaultCredentialsProperty in the definition of the Gift.aspx control to specify that authentication uses the default credentials of the currently logged on user.
Note: For ASP.NET applications, the default credentials are the user credentials of the logged-on user or the user being impersonated. See the MSDN documentation for System.Net.SmtpClient Class.