Although there is much good stuff in this thread, it looks to me as
though people are missing the point of the box under discussion - or I
have got hold of entirely the wrong end of the stick....
This is a fallback delivery box, is it not?
So there are no local users to deliver to.
The only mail coming into it is from your own outgoing MTAs which have
already attempted to deliver the message and been unable to.
By definition this box is only getting the least deliverable messages.
Which would make me wonder about the idea of very frequent queue
runners (but feel free to show me this feeling is wrong).
You do want to ensure that messages have been routed, so that when a
delivery succeeds, another message can be attempted in the same session.
Tweaking of timeouts to avoid tarpits may be useful.
Nigel.
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[ Nigel Metheringham Nigel.Metheringham@??? ]
[ - Comments in this message are my own and not ITO opinion/policy - ]