New Code!
Postoffice has been pushed up to version 1.3.6, not to fix a bug (amazingly enough), but to add a new feature.
The escape-from option in postoffice.cf tells postoffice -- when delivering mail locally -- to scan the body of incoming messages for lines beginning with the pattern 'From ' and prefix them with a > character. Why? Some mail readers (I've gotten a report that Mozilla Thunderbird is one of them) can't handle naked 'From ' lines in messages, and will break them in two. This feature (escape-from=1 in postoffice.cf) should fix that wagon.
Note that this code is not extensively tested. I use mutt, which is a pretty sucky mail reader, but at least it's a sucky mail reader that can handle embedded From lines, so I don't many places where I can exhaustively test this code. "It works for me!" is still my line, but "It works" covers a pretty small area right now.