We currently run a mail server using Postfix and Amavisd.
A client has asked us to see if we can archive all of their internet email and we had started with using the Postfix always_bcc option.
However, we have come to realize that when emails include BCC's, all of theat information is not proeproly preserved. The always_bcc message only has the TO: and CC: fields.
In our instance, the client mail server uses Postfix for smarthosting and at this point, I'm sure that the BCC information is intact when sent to the Postfix server. The logs will show the email going to the TO:, CC:, and BCC: field all using the same Postfix ID so I'm pretty sure the information is there.
I have recenly been looking at qpsmtpd as another option for capturing this information and trying to see what other otpions I may have for preserving tand archiving the email with the info.