Hi Denis,
I expected that when I send a message to alias+det...@mydomain.tld, it would go into the "detail" folder of u...@mydomain.tld. However, it goes into the INBOX folder of u...@mydomain.tld. Is it the intended behavior?
It is. To achieve the desired folder, you need a sieve script: https://wiki.dovecot.org/Pigeonhole/Sieve/Examples#Plus_Addressed_mail_filteringEnsure that you also subscribe to newly created mailboxes (lda_mailbox_autosubscribe=yes).
Best, Anton