[Dovecot] Sieve puts incoming message into inbox on any problem with submission_host

[Christian Rohmann]

Hello dovecot-users,

I have a question/suggestion regarding the submission_host feature of
the lda (either via dovecot-lda binary or lmtp) in combination with sieve.

When trying to deliver message to a mailbox and this message has a sieve
redirect action applied to it, dovecot is using the configured smtp
server to forward the message just fine. Unfortunately, if the server
configured for submission is unavailable, returns an error or cannot be
found via DNS, sieve will simply put the message into the inbox and be
done with it:

--- dovecot.log ---
dovecot: lda(user1): Error: lmtp client: DNS lookup of
idonotexist.example.com failed: Name or service not known
dovecot: lda(user1): Error: sieve: msgid=unspecified: failed to redirect
message to <user2> (refer to server log for more information)
dovecot: lda(user1): sieve: msgid=unspecified: stored mail into mailbox
'INBOX'
dovecot: lda(user1): Error: sieve: execution of script
/mailboxes/user1/.dovecot.sieve failed, but implicit keep was successful
(user logfile /mailboxes/user1/.dovecot.sieve.log may reveal additional
details)
--- /dovecot.log ---

The same applies to vacation messages being sent out. Especially with an
(unconditional) redirect action, users don't expect to find messages in
their inbox. Also problems with the submission_host could very much be
temporary and a little delay in delivering a message is better then
putting it somewhere the user doesn't expect a message to be.

Is there any way to change the behavior of dovecot or the sieve plugin
to tempfail in case a message cannot be sent out?
I know that with multiple sieve actions it gets more complicated as
there could be corner cases were the first message can be sent via the
submission server and another message produced by the same sieve script
cannot.

I'd love sieve to behave like this:

a) if submission host is unreachable (hostname wrong, timeout, ...) ->
tempfail

b) if submission host returns 4xx error -> tempfail

c) if submission host returns 5xx error -> fail(-save) and just drop the
message into inbox or even have an option to reject the message
completely in this case.


In case of a tempfail response, the mta simply queues the message and
tries again later. In case of a permanent fail the mta will create a
bounce message to in form the sender.





Regards and have a great weekend,


Christian