(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).
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).
Login to the FXOS chassis manager.
Direct your browser to https://hostname/, and log-in using the user-name and password.
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We have configured the outside and inside Interface with official ipv6 adresses, set a default route on outside Interface to our router, we also have definied a rule , which also gets hits, to permit tcp from inside Interface to any6.
In Syslog I also se...