Ok, this is a weird one..
I have a hostname "smtp.mydomain.com", that has multiple A records.
Some of those A records point to one host, some point to another. Both
are running identical exim configurations, which relay outbound for our
networks, accept relay for our domains (via
relay_domains_include_local_mx), but accept no local mail.
If I have:
somedomain.com. MX 10 mail.somedomain.com.
somedomain.com. MX 20 smtp.mydomain.com.
Everything works as expected. if mail.somedomain.com is down
smtp.mydomain.com gets the mail, and retries mail.somedomain.com until
either it makes it or retry expires.
Now, the twist. Some of our customers for which we either do primary
and backup MX, or just backup MX, have someone else running the primary
DNS for their domains. To facilitate my moving these around without
having to explain to some (usually clueless) DNS operator (usually
running NT) what an MX record is and why I need it changed, I have them
install something like this as their MX records:
theirdomain.com. MX 10 theirdomain.com10.mx.mydomain.com.
theirdomain.com. MX 20 theirdomain.com20.mx.mydomain.com.
and then
theirdomain.com10.mx.mydomain.com. CNAME mail.mydomain.com.
theirdomain.com20.mx.mydomain.com. CNAME smtp.mydomain.com.
so that I can change the CNAMES quickly if/when I need to.
However, when I do this, the two servers that are "smtp.mydomain.com"
play hot-potato with the message every retry cycle, until eventually
there are too many Received headers and it bounces.
How can I tell the two servers that are "smtp.mydomin.com" not to pass
mail to each other, under any circumstance?
---------------------------------------------------------------------
David J. Chiodo \ Microwave Systems \ Campbell Network Systems
<djc@???> <davec@???> \ 820 Monroe NW Ste 411
Domain Administrator <dns@???> \ Grand Rapids MI 49503
Customer Support <support@???> \ 616-774-3131 <info@???>
Fax 616-774-3933 Tollfree 1-888-694-INET http://www.cns.net
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