No vacation notices for adresse at alias domains
The log will say
Apr 5 17:23:45 server dovecot: deliver(user@domain.example.com): sieve: msgid=<...>: discarding vacation response for message implicitly delivered to user@aliasdomain.com
Problem here is that the generated sieve script is missing the alternative email adresses in :addresses, see http://wiki.dovecot.org/LDA/Sieve#Vacation_auto-reply-1