What is the desired behavior if person A posts to a mailing list, and person
B follows up, etc etc - and then person G replies to F, trims out persons
A through E, and does a *BCC:* to the mailing list?
People do this as a crude way to control followups. Given widespread
support for a followup field, why would someone do such a Bcc?
The normal use of a blind copy is to add someone to the envelope
recipient list, without affecting what the (non-blind) recipients see.
So, in general, a Bcc isn't relevant to the rest of the header.
a bcc: to the author because his list membership is unknown
That's arrogant behavior. Your followup is important enough to get to
him, but subsequent followups aren't?
Given widespread support for a followup field, you won't have to do this
sort of guesswork.
Let your users manage their own mailing lists. http://pobox.com/~djb/qmail.html