@msimerson this change causes a regression in our tests. the mx hook is not registered anymore if enable_outbound is false. Is this intentional ? The mx hook is how the per-domain relay configuration is loaded.

61126ab#diff-358fdbf915639f898db16fb2bab56c2284331a4e8bfe65e25fe3b0f1f13bdcfeR33

To add some more info, the way we configure the forwad plugin is:

enable_outbound=false
domain_selector=mail_from
[cloudron.addon]
enable_outbound=true
host=172.18.0.1
port=2587
enable_tls=true
auth_type=plain
auth_user=relay_user
auth_pass=relay_pass

With the above config, emails fromxx@cloudron.addon are not forwarded to the relay.

if enable_outbound is false. Is this intentional ?

Well yes. Sorry. The get_mx hook doesn't forward (in the sense of the smtp_forward plugin) at all. Instead, messages are accepted into Haraka's queue and then delivered with outbound. The get_mx hook can then provide a more specific route to outbound. But it's really not forwarding, it's MX routing, right? And so get_mx should be controlled by outbound_enabled.

That's what I was thinking. But I missed something important: that disables the ability to have [outbound] forward MX routing disabled in the main config and enabled per-domain. And vise versa. #3204 does the needful, but it needs to have a test added so prevent future regressions. smtp_forward is used in quite a few ways (I also [ab]use it to deliver via LMTP using outbound).

But I missed something important: that disables the ability to have [outbound] forward MX routing disabled in the main config and enabled per-domain

Yes, indeed, this is exactly how we were using it. I see you already reverted that part of the code, thanks! I will test and get back.

Can confirm your revert fixed the issue (for us).