What I could investigate so far is that there seems to be some major issues with IMAP handling with Courier IMAP. I already saw some people running into the same problems:

1) Not being able to view unread messages (I get 500 error on our server) which is a problem with the Courier IMAP version being delivered with Debian sarge and RC's IMAP handler class from my guess.

2) Also on my installation the default special IMAP folders like Sent, Trash, and Junk are not shown as "special" as they should be.

I didn't find time to investigate neither first nor second issue any closer, but I hope I'll find the time beginning of next week.

If somebody has already posted solution or any more detailed description, forget about this one.

Regards,

Rob