Postfix and Mailscanner sitting in a tree k-iss-ing

[Drew Marshall]

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avery wrote:

<Snipped>

>
> Good inforamation, thanks for the advise. But I am also interested in
> the reasons why the method in which Mailscanner and Postfix work
> together has changed in the last few months. What were the reasons in
> changing this? At one time postfix needed to run in 2 instances one for
> incoming and one for outgoing. This does not seem to be the case
> anymore. It seems to be some top secret reason that no one knows about.

Not that secret really. Postfix, being of 'modular design' relies on a
beast known as queue runner (You will find manual entries about it and
an entry in master.cf which controls it). Basically the queue runner
moves messages about to the different bits of Postfix e.g. smtpd
receives the message, the queue runner moves it to an out going queue or
delivery agent, you get the idea. Now Wietse (Sorry if that's spelt
wrong but it's Christmas and I can't be bothered to look it up ;-) )
doesn't feel the need to use any form of locking on any of the queue
files as from his perspective the only thing moving messages is Postfix
(And probably the queue runner at that) so there is no need to lock
files from it's self. That's fine until you introduce MailScanner who
will pick up messages and scan them and quite possibly while the queue
runner is trying to move them, hence making duplicate and truncated
messages (Which is the complaint from the Postfix community). The
solution is quite simple. Put the unscanned mail some where that the
queue runner doesn't ever go - the hold queue. From there MS can do it's
bit with out fear of interference and then MS moves the message from the
hold queue back into an active queue for delivery. That is the 'secret'
of single verses double Postfix instances.

Hope that makes it clearer.

Drew

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