mbox - maildir transition using dovecot lmtp local user auth struggles

Approaching age 49 I passed the time long before when I was excited about
a new version or a software upgrade. Why poke something that works?
>From time to time I'm forced to upgrade hardware and software against my
will otherwise could serve many more years.

I became the victim of mbox -> maildir transition. First I converted the
good old Sendmail to Postfix. Initially it still used procmail delivering
in mbox mailboxes, now I converted the mboxes to maildir and changed the
way of delivery by dovecot lmtp, since that is the software I use for IMAP
access. At least there seem to be no data-loss after a couple of doveadm
backup and sync retries.
There are just 4 local users, so dovecot was set for pam authentication
and it worked (for 20+ years, although there were some bumps while
upgrading from 2.3 to 2.4 syntax). Now dovecot lmtp started bouncing
mails, because it was trying to authenticate a username including the
domain name as well and the backend returned unknown user, since expected
local user names. This wasn't a problem with mbox/procmail. I asked AI for
help and first suggested to use auth_username_format = %Ln. It soon turned
out, that this syntax is obsolete. So I dig into it myself and tried
auth_username_format = %{user | lower}. It wasn't picked up by dovecot,
symptoms persisted. I also tried auth_username_translation = %{user |
split('@') | list_first}, which turned out to be also unsuccessful.
I also tried to solve the issue on the postfix side by introducing regex
handling, but either lmtp_generic_maps = regexp:/etc/postfix/lmtp_generic
or recipient_canonical_maps = regexp:/etc/postfix/recipient_canonical had
no influence on the symptoms (regex was: /^([^@]+)@atoth\.sote\.hu$/
${1}). Also tried virtual conversion and lda. Nothing solved the fricking
problem.
I ended up using a workaround I'm ashamed to share. I kept passdb pam, but
for userdb I created a userdb-file, where I included users both with the
local name only and the full email address. This shameful concept is
functional, but I have to admit it is disappointing: several ways back and
forth for solving an issue were all unsuccessful. And it is exhausting.

Any ideas appreciated.

BR: Dw.
-- 
dr Tóth Attila, Radiológus, 06-20-825-8057
Attila Toth MD, Radiologist, +36-20-825-8057

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