BCC Headers in MDaemon
BCC by definition is blind. The header should never be created by a mail client because the message should not display that it was sent to anyone in the BCC field. Here's what the headers look like when composing a message with a BCC:
Received: from robin ([192.0.2.124]) by test.mail ([192.0.2.124]) with SMTP (MDaemon.PRO.v9.6.6.R); Fri, 20 Aug 2010 10:09:15 -0400
Reply-To: 'Blake' <firstname.lastname@example.org>
From: 'Blake' <email@example.com>
There is no BCC information in the message even before it goes out to the Internet for delivery. (for example BCC'ing firstname.lastname@example.org)
The way that BCC mail is routed is via the SMTP envelope information. Mail servers pass the message along via SMTP and the delivery information is kept in tact.
When you download the message via DomainPOP, MDaemon does not have the SMTP delivery information any longer. It has to make the best guess as to where the message should go.
Some ISPs stamp a header so that the SMTP delivery information is available for parsing, but it's not required. These headers may be “Envelope-To” or “Delivered-To” or something similar. Your ISP may be able to do something along these lines. Alternatively you could ask them if you could receive mail via ATRN instead of POP because then the SMTP envelope is still there.