[Mimedefang] SMTP mailertable question

Cormack, Ken kcormack at acs.roadway.com
Tue Dec 30 10:36:46 EST 2003


I have a similar environment, here.  My internal host uses the sendmail
"SmartHost" functionality to forward outgoing mail to my one of my DMZ
relays, since the internal machine can only see the Internal DNS.

My problem, like yours, is that I have a pair of relays in my DMZ.  I wanted
the internal host to be able to send outbound mail to the secondary system,
in the event the primary was down.

Had I been industrious, I could have created some kind of heartbeat address
in a quasi-HA configuration... an address that would exist on the primary,
yet be moved automatically to the secondary system when a primary outage was
detected.  This was much more involved than what I needed.

So, I just threw together a generic name in the /etc/hosts file of the
internal machine (so I could manipulate it independent of the internal DNS,
since only the internal smtp host would be referencing it.)  I then set up a
cron script to check port 25 connectivity to the primary machine every
couple minutes.  As long as the primary machine responded, my dummy name in
/etc/host reflected the IP address of the primary machine.  If the primary
machine's IP address failed to respond, the script toggled the /etc/hosts
entry for the dummy name such that it would now point to the IP address of
the secondary server.  The script gave preference to the primary server,
meaning that if the dummy name was pointing to the secondary system's IP
address, and the primary's address came back online, the script would toggle
the dummy name back to the primary machine's IP address.

It would be nice if the sendmail folks would allow "SmartHost" to contain a
list of hosts to be tried in sequence.  But in the meantime, a hack such as
mine, though certainly not pretty, works quite well.

Ken

-----Original Message-----
From: mimedefang-bounces at lists.roaringpenguin.com
[mailto:mimedefang-bounces at lists.roaringpenguin.com]On Behalf Of
WBrown at e1b.org
Sent: Tuesday, December 30, 2003 10:25 AM
To: MIMEDefang, 
Subject: [Mimedefang] SMTP mailertable question


If I have a clustered mail server behind my mail filter, how would 
configure the mailertable to deliver messages to server1, but if it is 
down, deliver it to server2? Something along the lines of MX records with 
different preference values.  If I wanted to use DNS, I would have to set 
up separate DNS servers just for the mail filter and I'd rather not go 
through that effort.

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