Re: [exim] Forward from external immediately without queue

On 23/12/2020 19:25, Yves Goergen via Exim-users wrote:
> So I had another idea. If queuing and bouncing is the problem, can I get rid of that?

Slight terminology diversion... "store-and-forward" is a better description
of the cause of your problem. Exim generally tries to deliver forwarded
messages as son as it can; they do live in the queue for that very short
period until the onward delivery completes - but barring errors we don't
generally regard it as queueing.

> If a message comes in from an unauthenticated sender, that must be another mail server. Those have got time, there's nobody waiting in front of a screen for the message to be submitted. So could Exim just try to deliver the message immediately in this case? If that fails, it could directly reject the message in the waiting original connection. No need for bounces.

What you're interested in is "cutthrough routing". It's in the docs.

> If the remote error is permanent, so should be Exim's. Same for temporary errors.

Yes

> Passing back the remote error message is probably a privacy concern as it might disclose the forward address or provider.

This could be a problem for you.
>
> This must only apply to forwards for unauthenticated senders. Authenticated senders are my users, they provided a password and I know I can send them bounces safely. And they're waiting for completion of the submission.

It'll work for either. But some MUAs don't like getting SMTP-level
rejects, so I tend to agree with you, assuming that your set
of authenticating senders as the same as the set of MUAs that
you're providing submission service for.

> How would a configuration of this look like? Or where in the documentation can I find more information about that?

Write ACL code that identifies suitable messages then requests cutthrough
routing for them.
--
Cheers,
Jeremy