Your code looks good, so I would suggest that the bug is either in the MailMessage object, or in your e-mail server. You could track down which one by:
1. Connect to your e-mail server using an existing e-mail client (thunderbird or similar). Send a message with a BCC, and see if the server actually sends it off.
2. Save your e-mail to a file. There is a reasonable article here (
Adding Save() functionality to System.Net.Mail.MailMessage[
^]) to show how to do that. Make sure the BCC headers are there.