I'm fairly sure that gnus/imap/agent/expiry is, um, *verb*ing mail

[Wes Hardaker <wes@hardakers.net>]

I turned off the agent a while back because I thought it was causing
problems with older mail getting deleted.  I'm was quite convinced
that was the case again, as I just added my imap server back as an
agent to speed up group entry, as has been discussed here in the last
few weeks.  After an expiry process finished:

  ; relevant settings:
  (setq gnus-total-expirable-newsgroups "nnimap\\+server:mlists")

  ; done when idle:
  (gnus-group-expire-all-groups)
  (gnus-agent-expire)

I entered a mailing list that did *not* match the above expression,
and noticed that the summary was a ton shorter than normal
(specifically, the read mail (but not marked as expirable) was no
longer shown).  I figured gnus had deleted the mail again and my
earlier suspicions were confirmed.  Entering the group with a C-u to
double check showed the mail still missing.

This time, however, I went to the server buffer, removed the agent
from the imap server and re-entered my group to find that all the old
mail (read) reappeared but so had every other message that was marked
as expirable but was now no longer marked that way.

So, my best guess is that for !total-expirary groups:

  1) the agent doesn't honor the gnus-total-expirable-newsgroups flag
     and deletes the headers from its cache.

  2) While doing so, it somehow also removes the E mark for every
     article as well.

  3) this leaves things in a state which means:
     a) the agent's cached headers don't contain stuff for every
        article that is really in the backend (imap).
     b) if the agent is removed from the process, the previously
        marked articles have lose their expirary mark.

Help?
-- 
"In the bathtub of history the truth is harder to hold than the soap,
 and much more difficult to find."  -- Terry Pratchett