On Mon, Jan 05, 2004 at 04:57:43PM +0000, David Woodhouse wrote:
>
> We could in theory do just the same for DATA -- if the real target is up
> and running we can attempt to deliver the mail immediately, and if it's
> rejected the relay can _also_ reject it immediately, rather than storing
> it and then being expected to (attempt to) bounce it.
>
> In the case where we're a 'protective' relay for a machine which is
> expected to be up and running, and where we are already doing recipient
> verification callouts, we could theoretically use the _same_ connection
> to actually _deliver_ the mail.
I recently suggested a feature to Philip that I've called early_delivery.
This would be a modifier for use in the DATA ACL, which would cause a
delivery attempt there and then. You'd be able to detect these early
deliveries using an early_delivery router condition similar to the
verify and address_test conditions.
The motivation for this was to be able to pair up MX machines so that
each one has a shadow machine that receives a copy of all its email.
If the machine dies then any messages that were stuck on its queue can
be recovered from the shadow, rather than being lost. Or if a destination
machine dies after receiving a message (so the MX has deleted it) it
can be recovered from the shadow.
However the feature is troublesome from an architectural point of view
(Philip wants to keep reception and delivery more separate than this)
and w.r.t. how it fits in with local_scan() and the system filter.
I'd also be wary to use it between systems that aren't tightly
coupled (such as a departmental email server and our central email
relays).
I have some notes about it on the web at
http://www.cus.cam.ac.uk/~fanf2/hermes/doc/misc/hr-exim.txt
Tony.
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