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From: DAVID HASSILEV on 25 Jan 2010 13:08

Hello, I have tried to search through the list archives but have not found
what I'm looking for so I thought I'd post to the list.

I currently use MS Exchange to provide outbound email a dual route based on
both a cost metric as well as message size that ultimately goes to the same
smart host, though to different IP's over different transports. I would like
to accomplish the same thing via Postfix if it's possible.

For discussion; I have two connectors configured in Exchange, connector 'A'
with a cost of 100 and a size limit of 500Kb. Connector 'B' has a cost of 10
and size limit of 200Kb.

Connector 'A' is a public IP but for this discussion we'll say
192.168.10.10.

Connector 'B' routes to the same physical smart host but behind our
firewall and with a private IP. We'll say 10.10.99.10.

In this way, outbound email that is less than 200K will queue via 'B' until
it times out, at which point it will be automatically moved to travel via
'A'.

Traffic that is over 200K but less than 500K will queue via 'A' and stay
there until delivery attempts are exhausted.

We need this because our bandwidth is very limited over transport 'B' and
thus to keep the queues from backing up, the tight 200K limits are
necessary. It is further mandated since our larger bandwidth over connector
'A' is unreliable and sometimes will not be available at all (for days or
weeks). We can tell users that larger emails (typically with attachments)
may take hours or even a day or two to be delivered while smaller emails fly
through generally in minutes because the queue is kept clear.

Can someone please tell me if there is a mechanism within Postfix to
achieve similar results or at least point me in the right area to look at
possibly writing my own scripts? I am a postfix neophyte (though not
unfamiliar with having to customize Sendmail way back when). I'm just not
clear if I were to write a script, where can/should I hook it into Postfix.

I am also open to suggestions for COTS products that could serve this
purpose. I am hosting on OSX 10.6 and currently using an exchange server
simply as a router. There must be a way to get rid of the exchange box!

Regards,
-David


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