nnimap displays wrong article after server move (Was: "Ghost count" on nnimap group after server move)

[Steinar Bang <sb@dod.no>]

Summary:
 - I have moved my IMAP server to a different machine
 - Both machines running dovecot on debian 11.6.
 - I have rsynced config and mail from the old server to the new
 - I see weird behaviour in Gnus after the move

By "weird behaviour", I mean:
 - The count issues mentioned earlier in this thread
 - Missing articles (articles I thought I had seen in gnus were gone
   from the Maildir, when I looked into the Maildir on the server)
 - Re-appearing deleted articles (some spam articles I was sure I had
   deleted in gnus with "B DEL" were still in the Maildir)

I thought the problem was in the server: something in the dovecot.*
files in the Maildir directories maybe.

But then I switched off the gnus agent for that IMAP server and I saw
different kind of strange: In the group summary, I saw the same articles
I saw in the Maildir, which were not the same articles I saw with the
agent present.

I tried sending some messages from my work address.

The messages arrived, and looked right in the summary:
R  [   5: BANG Steinar           ] Test fra jobben til meg hos bang 1
R  [   5: BANG Steinar           ] Test fra jobben steinar at bang 2

But the content of the messages were older messages, eg. for the first
one (wrong subject, wrong text in the body 1and wrong date), with
anonymized email addresses:
 From: BANG Steinar <steinar.bang@mycompany.com>
 Subject: Test fra jobben
 To: "sb@mydomain.no" <sb@mydomain.no>
 Date: Tue, 7 Feb 2023 22:08:52 +0000 (3 days, 13 hours, 12 minutes ago)
 Attachment: [3. text/html]...


 Kommer denne fram?

So then I thought: is it my client?

So I installed thunderbird and added the server credentials, and yep, I
saw the same files I saw physically in the Maildir.

So yep, definitely my client.

So in case someone wonders: Moving from one dovecot to another, using
rsync for dovecot config and the mail content, and switching the server
in DNS, while keeping the config on gnus (agent disconnected until the
DNS alias had switched), probably doesn't work.

There is something funky with the article ids probably?

That's why I saw articles in the agent that no longer were present on
the server, and saw articles I thought I had deleted. I had "B DEL"'d
the wrong articles on the server.

So will need to sync up gnus to the current server somehow?

Why do I get the wrong articles?

Can gnus be loading the agent articles even though I stopped using agent
for that server?

Things to try:
 1. Stop gnus and rename the agent directory for the server
 2. Delete all groups from the server and stop gnus and then restart
    gnus on a different emacs (to ensure nothing is cached in memory)
    and readd the groups

I'll do the above anyway, but if someone have suggestions to things I
should have done instead, then I'll be happy to hear them (even if they
come too late for me).