handling unknown recipients

[Tilman Schmidt]

Running Postfix with amavisd-new and quarantining attachments seems to
produce an unfortunate interaction when mail with a banned attachment
arrives for an unknown recipient:
Amavis checks the mail for banned attachments before checking whether
the recipient exists.
If $warnbannedrecip = 1 it then proceeds to emit a notification about
the banned attachment to the non-existing recipient, which promptly
bounces to the notification sender address, typically an administrator.
If $warnbannedsender = 1 the sender gets notified that her mail was
quarantined without mentioning that the recipient doesn't even exist.
Neither result is desirable.

Is there a way to validate the recipient address before bothering with
the content of the mail?

TIA,
Tilman