courier-imap-3.0.5 is currently marked stable but it breaks the OUTBOX feature. According to the courier-imap ChangeLog:
2004-07-12 Mr. Sam <firstname.lastname@example.org>
* outbox.c (is_outbox): Make OUTBOX work again.
This is pretty important for many people using courier-imap, particularly with offlineimap. Can we get a stable push on 3.0.7?
3.0.7 has all the stable keywords that 3.0.5 has. Closing.