Re: Value of backup MX

[John Goerzen <jgoerzen@complete.org>]

On 2004-11-09, Steve Drees <drees@rangebroadband.com> wrote:
> John Goerzen <> wrote:
>> I'm looking at redoing my mail setup due primarily to spam filtering.
>> Over at http://www.tldp.org/HOWTO/Spam-Filtering-for-MX/multimx.html,
>> they are suggesting not to use redundant mail servers unless needed
>> for load balancing.
>
> This is poor advice.

Could you elaborate a bit on why that is?  The author is saying that
well-behaved (ie, non-spamming) MTAs would keep retrying for several
days anyway, so the only time a backup MX would really prevent mail loss
is due to an outage extending more than that time.  What do you think?

>> It seems to make a lot of sense to me, but it seems too that I must be
>> missing something.
>
> I'd suggest having a backup MX but make sure you have all the filtering at
> your backup that you have at your primary.

That's what I have now, but there are some things that can't be done so
well (or at the very least, only in a horribly kludgy manner).

For instance, if somebody sends a message to
nonexistantuser@complete.org, and it goes through the backup MX for
whatever reason, the backup MX accepts the message.  When it gets to the
main server, it will reject it with a 550.  The backup MX then has to
e-mail back to the sender a bounce message.

Now think what happens when viruses/spammers do this.  My backup MX is
sending out a lot of bounce messages to potentially innocent victims for
this reason.

-- John