[Dovecot] LDA: handling non-existent mail dirs

We have users existing in LDAP but not supposed to receive mail. We used to handle that (somewhat ungracefully) by simply not creating the top mail directory for those accounts. Since switching to Dovecots LDA, these non-existing dirs are considered temporary failures and so the junk mails pile up in postfix' queue

Would it be possible for deliver to optionally treat this as a permanent error?

I know the clean solution woud be checking for an LDAP attribute in postfix before even accepting the mail.