Boy, everytime this comes up we end up repeating ourselves :)
Everyone knows we need to be able to initiate threads and reply to them via e-mail, and no one knows why aD's one implementation of this was for ACES (the platform Michael Feldstein was referring to). ACES doesn't use bboard but rather a truly ugly hacked thing based on the general-comments module, so the work they did doesn't work with bboard. Grrrr...
I think integration with qmail is the right thing to do, given that so many ACS users are familiar with it.