I found that if someone sends to user@???, the only
default router fails, and the message gets frozen for the
reasons unclear to me.
Is there some "standard" (inexpensive) way to bounce
everything that didn't match any router back to the sender,
with no postmaster intervention?
In general, there might be some more explicit logics
with freeze-bounce-delay behaviour, no_freeze_on_failure
or something.
Thank you,
Ilya