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));
}