Hi,
In the event that the local delivery fails with a 5xx error, OpenSMTPD
queues the message for retry (and eventually supplies the sender with
a "delayed" delivery notification, etc). My naive expectation is that
SMTP 5xx means permanent failure, so an immediate bounce would be more
appropriate.
(if I read it right) according to RFC 1893 both codes should be treated
as permanent failures. I don't see anything in RFC 2033 that would
negate that for LMTP.
Having said that: Accepting a message as an MX only to immediately let
it bounce is bad practice. I have last seen such a setup 15 years ago.
Where the MX would accept mails for subdomains it had no mailbox-
knowledge. Before the system was finally overhauled 90% of the data
centres internet upload was bounce messages! Insane!
Think about it. Your setup accepts everything. It takes responsibility.
Now it turns out the address can't (for what ever reason) be delivered
to. Your system has to inform the sender. If you hadn't accepted the
mail, the responsibility would still lie with the senders system and not
yours.
If the MAIL FROM was forged the bounce messages could go to a
non-involved party. To them it could look like your system is sending spam.
If you get hit by a spam-wave in the form of
$every_name_in_the_b...@example.com. Your system will give the spammer
positive feedback for seriously every address. Not only will they come
again. Your system will send thousands of bounce messages to god knows
where.
You should seriously bring the mailbox status to the front!
