Support relaying to an LMTP endpoint

[gahr]

This adds support for speaking LMTP to the relay. It's useful to bypass MTAs in case an LMTP-aware service, e.g., Dovecot, is running locally-ish.

[corecode]

what happens when a mail can't be delivered by the lmtp server? is this a reasonable configuration, lmtp server without SMTP server?

[gahr]

is this a reasonable configuration, lmtp server without SMTP server?

No, I think you'd typically have both. But this allows not to expose unauthenticated SMTP and avoid deploying auth.conf. At the end of the day, this is about skipping the middle hop in the dma -> smtp -> lmtp chain.

[gahr]

what happens when a mail can't be delivered by the lmtp server?

In my smoke test, I send an email to 3 recipients, 2 valid and 1 invalid. The 2 valid recipients got the mail.

[gahr]

what happens when a mail can't be delivered by the lmtp server?

In my smoke test, I send an email to 3 recipients, 2 valid and 1 invalid. The 2 valid recipients got the mail.

And for the failed one, you get a nice delivery failure:

imap.example.com [192.168.1.120] did not like our RCPT TO:
550 5.1.1 <foo@example.com> User doesn't exist: foo@example.com