File attachments in Mail in WPF

 Microsoft.Win32.OpenFileDialog dlg = new Microsoft.Win32.OpenFileDialog();
                dlg.FileName = "Document";
                dlg.DefaultExt = ".txt";
                dlg.Filter = "Text documents (.txt)|*.*";

                Nullable<bool> result = dlg.ShowDialog();

                if (result == true)
                {
                    string filename = dlg.FileName;

                    mMailMessage.Attachments.Add(new Attachment(filename));
                }