Hello everyone,
I've recently upgraded to debian trixie, which includes postfix version
3.10.3 and dovecot version 2.4.1-4.
After updating my dovecot config I realized that receiving mail to
aliases was broken, due to postfix not resolving aliases before using
dovecot's quota service. Since aliases are not real users this causes
the lookup to fail, leading to the error "554 5.7.1 - Recipient address
rejected: Unknown user".
It's possible to solve this by removing the check_policy_service
directive from smtpd_recipient_restrictions, but this causes quota
queries to happen after the mail is enqueued and risks backscatter.
Since my mail server is for personal use and I do not use quotas at the
moment I opted for this approach.
Searching the web a bit I found this comment on docker-mailserver github
where they encountered the same issue:
https://github.com/docker-mailserver/docker-mailserver/pull/2248#issuecomment-955088677
The above link likely explains it better than I have here, and it seems
their solution was to use dummy dovecot accounts, which is not a general
solution, e.g. it doesn't work if an alias points to another alias, or
for catchall aliases.
Another option is to configure dovecot quota service to tolerate unknown
users, but this again risks backscatter if the alias resolves to a user
whose quota has exceeded.
I was wondering if there was an option to make alias resolution happen
before the quota service is queried.
Cheers,
monodev
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