Exlude non-SMTP services from local_mx_ok

[analogic]

The idea of cfg.local_mx_ok is ok, but with LMTP local delivery enabled this option makes no sense.

I've come up with a solution to "filter" only destinations with port 25, as other ports are AFAIK only used in a custom defined way and therefore wanted. The original purpose of this option should be preserved as these loops only happen with SMTP. Another way could be to just check using_lmtp, but maybe there are other protocols?

Checklist:

• [ ] docs updated
• [ ] tests updated
• [x] Changes updated

[msimerson]

This is an improvement, but this uses port 25 as a proxy for determining "is this message capable of being delivered locally." Right? Because mail routing is so flexible, even this is bound to have edge cases.

Maybe just check for queue.wants? If it's set, then some plugin has already determined that there is a known forward path (which is likely local).

I devised queue.wants and queue.next_hop to permit any type of complex routing. The idea is fairly easy to grok (I think): queue.wants is the name of the plugin/entity that knows how to properly deliver that email message. The next_hop is a URI used by that plugin to direct the delivery.

The smtp_forward and qmail-deliverable plugins each do some form of recipient validation. When they do, they may specify the queue.wants and the queue.next_hop options to control routing. Examples:

plugin	queue.wants	queue.next_hop	example
smtp_forward	smtp_forward	as configured in smtp_forward.ini	smtp://172.16.15.8:25/
qmail_deliverable	outbound	lmtp (for mailboxes)	lmtp://172.16.15.15:24/
qmail_deliverable	outbound	smtp to qmail (for aliases, forwards, mailing lists)	smtp://172.16.15.8:25/

At queue time, all the queuing plugins (and outbound) check for the presence of queue.wants. If it is set and the value isn't for itself, that queue plugin bails out so that the correct queue plugin can process the message.

[analogic]

You're right Matt, I'm a bit blindfolded by my usecase - obviously this patch won't work for smtp forward and qmail deliverable.

I think a queue.wants check would be good enough, and certainly more usable than the whole local on/off thing. But I've been investigating how to implement this, and have come up with an idea to make it simpler and achieve the original goal. What if we only apply the local block to last resort routes in hmail.js? Adding the "default: true" flag and checking those routes should be enough...

[analogic]

closing => #3307