C350 sends to MX with lower prio -> mail loop

Unanswered Question
May 27th, 2009

Good evening.

Please consider the following setup:

Internet -> |Ironport C350| -> |inner Mailgw| -> |Messagestore|


MX record are:
20 smtphost.ise.fraunhofer.de. <-- inner Mailgw
50 ipo1.ise.fraunhofer.de. <-- Ironport C350
200 mailgw1.fraunhofer.de.
200 mailgw2.fraunhofer.de.
210 mailgwb1.fraunhofer.de.

(mailgw[1,2,b1] are backup gateways and .fhg is short for .fraunhofer)

The following problem occured when we switched off our inner mail gateway for maintenance: ipo1.ise.fhg.de received mails, could not reach smtphost and then routed them to mailgw1.fhg.de, which in turn handed them back to ipo1 and so on and so forth until the hop limit was reached.

Maybe I've misinterpreted the RFC2822 but I always thought that once a mailexchanger got a mail ii should never forward it to another mailexchanger with a lower priority (higher number).

Any ideas?

Cheers,
Hubertus

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steven_geerts Tue, 06/02/2009 - 21:24

Hi Hubertus,

I’m not sure I understand your infrastructure completely. Are all of these hosts reachable from the internet? In that case your Ironport will not handle the majority of your mail traffic if your internal system is operational.
Another issue... I think (not sure) that MX preferences should not exceed 100.

As far as I know the behavior you describe is normal if you do not implement static routing on your systems.

Let’s assume that your inner Mailgw is not reachable from the internet but can be reached by all other systems. in that case the other systems should have a static route to "smtphost" only (for your internal domains).

Hope this helps.

Steven

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