user's mailbox is over quota, it neatly notifies Postfix.
Problem: the sender never gets notified that the recipient is over
quota, only postmaster (in our case). Even with Postfix 2.3 there
doesn't seem to be a way of setting error_notice_recipient to the
sender, rather than a system user, e.g. postmaster.
Or is there?
Solved ... it was a Postfix transport misconfiguration; sorry for the noise.