nnimap refuses to delete mail

[Guido Van Hoecke <Guido.VanHoecke@advalvas.be>]

The nnimap under Gnus v5.8.3 never removes any of my mail
messages. It pretends to do so, does never complain, but when I
revisit my Inbox (or any other imap folder from which I have
removed messages, either via 'G Del' or via
'B m some-other-imap-folder') all messages that were supposed to
be removed are still there.

I have (expiry-wait . immediate) for all folders, for some
folders I even use (auto-expire . t). This used to work during
the nnimap-beta phase.

I know that imap-servers sometimes are picky about deleting
messages. This usually happens if more than one imap session is
active for the same userid. And sometimes one gets stuck with
invisible backgound sessions (e.g. after closing Netscape
Messenger, but not closing Communicator, some mail checking
background task may continue to access the server).

I have carefully avoided such contention situations. But still
nnimap happily colorizes my summary lines as being deleted (in
case of the 'G Del' command) or puts the 'E' mark in my
auto-expire groups, gives me a message 'Setting marks in
INBOX...' or whatever folder, but, the messages never disappear.

This is not a general problem at the server: Netscape, Outlook
Express and Pine (http://www.washington.edu/pine/) have no
problems to delete messages. Pine never has any problem with
deleting imap messages (if the folder is not in use by another
imap process)?

I now read my mail with Gnus, and I have to expunge it with Pine
or Netscape or Outlook. And, as said before, Pine is the most
effective. It pains me a bit that such a simple straightforward
(no blame meant) program is better at handling messages.

Does anybody have an idea why this does no longer work?