From: Jimbo (jimjamesberwick.com)
Date: Fri Apr 25 2008 - 20:20:04 CDT

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René Nussbaumer wrote:
> Yes, I'm aware of this fact. However, a backup MX should take care of
> the mail if the primary is currently not reachable. At least from my
> point of view. Yes, their is the danger of producing backscatter but
> under normal circumstances the primary MX would not be that long
> unreachable
If you live in some perfect world where spammers don't exist, sure.
Spammers frequently target higher weight, lower priorty MX records
hoping to bypass spam filtering. The first time a spammer hits your
backup MX server and sends a few (hundred) thousand pieces of junk email
to your domains and they all generate a bounce message, what will you do
then?

Being a backup MX is no excuse to not have recipient validation. If you
are using reject_unverified_recipient and have caching turned on, you
can probably weather those few hours that the primary server is offline
without so much as a hiccup.

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