Re: [Exim] @mx_any and 127.0.0.1

On Thu, Apr 15, 2004 at 10:57:14AM -0400, Dickenson, Steven wrote:
> Brian wrote:
> > I am currently testing out exim and it's filtering functionality on
> > this domain but I usually set the MX entry of that domain to
> > 127.0.0.1, as well as all other requests.
>
> If you're doing this, why even both with an MX for the domain, or any hosts
> in the zone for that matter?

It's entirely valid to have a domain that will never send or receive
mail. The problem is that the lack of an MX record will not prevent
MTAs from trying to deliver mail to that domain: they'll just fall back
on the A record. If someone forges that domain in the return path on a
large batch of spam then a whole bunch of NDRs will be coming his way.
With no MX record, the MTAs will fall back to the A record and if there
happens to be one then a certain amound of time and bandwidth wasted
while mailhosts try to open smtp connections.

Setting an invalid MX record stops this.

--
Bruce

I unfortunately do not know how to turn cheese into gold.