[oclug] SendMail as a restricted mail relay

[Dave O'Neill]

On Tue, Nov 02, 2004 at 03:50:28PM -0500, Justin Wheeler wrote:
> While I don't know sendmail all that well, so I'll refrain from
> comment or trying to assist with that, I'm curious as to this "lowest
> mx not responding helps block spam" thing.

The assumptions here are:
   1) Everyone sending SMTP is RFC compliant (both legit MTAs and spammers)
   2) Spammers are stupid
Neither of which, unfortunately, is universally true.  Some MTAs will
continue to retry the lowest-weighted MX rather than trying to deliver
to a higher-weighted one, and some pammers frequently target
higher-weighted MX records in the hope that they might be less well
protected (some anti-spam software vendors charge per server).

> Perhaps I'm just speculating, but it seems to me that setting your
> lowest MX to an unresponsive host would do more harm than good.

Probably.  It may have some benefit, but there's a risk that you might
not get some legitimate mail, and that usually isn't acceptable.

Cheers,
Dave