[Mimedefang] Re: SMTP mailertable question

[Cormack, Ken]

Doing as you suggest with MX records, though it could be cool, requires the
creation of a seperate DNS domain.  And at the moment, our DNS is in a
transistion period as Active Directory is melded with BIND 9.  I am
reluctant to introduce new zones at the moment.  However, you got me
thinking about using the FALLBACK_MX host parameter.  It's almost brilliant.
I already use this in the DMZ, with my primary handing off to the secondary,
via FALLBACK_MX.  This "Spillover" arrangement has worked great, in the DMZ.

As I understand it, mail needing to go to an external domain would be
forwarded to the primary DMZ machine (via the SMARTHOST, which it already
does.)  However, in the event the first attempt to deliver to that host
fails, the FALLBACK_MX host would then be tried (my secondary DMZ host).

The problem is, the FALLBACK_MX host would also be tried, if one of my
several internal mail-hosting servers failed to respond.  Meaning, mail
coming in from the outside would get to my internal relay, and then possibly
be handed back out to a DMZ machine, only to ping-pong it's way between
hosts until the MAX HOP COUNT had been exceeded.  Not good.

Despite it's ugliness, I'll be sticking with the cron task for a while.
Although the DNS MX record games are far more elegant.

Ken

-----Original Message-----
From: mimedefang-bounces at lists.roaringpenguin.com
[mailto:mimedefang-bounces at lists.roaringpenguin.com]On Behalf Of Jeremy
Mates
Sent: Tuesday, December 30, 2003 11:22 AM
To: mimedefang at lists.roaringpenguin.com
Subject: [Mimedefang] Re: SMTP mailertable question


* Cormack, Ken <kcormack at acs.roadway.com>
> 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.

Set the SMART_HOST value to a DNS name that has MX records pointing to
each of the DMZ pairs.

$ host -t mx example.org
example.org mail is handled by 7 mx1.example.org.
example.org mail is handled by 7 mx2.example.org.

define(`SMART_HOST', `example.org.')

> 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.

define(`confFALLBACK_MX', `mail.example.org')
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