On Mon, Jul 25, 2005 at 09:12:42AM -0500, Stuart Johnston wrote:
> Bojan Zdrnja wrote:
> >
> >I completely agree with Gary. Rejecting e-mail for non existent users *at
> >the front-end* is a MUST.
>
> I thought that rejecting non-existent users at SMTP time was considered
> a bad idea because now the spammer knows that any messages that are
> accepted are valid email addresses.
I believe this was always largely a myth. While there was evidence
of a few spammers who actually winnowed out their lists, most do not.
I know a fellow who is a major anti-spam authority and maintains the
mail filtering infrastructure for a very large multinational
corporation. They went through a domain name change, as a part of
which addresses in their former domain name became inactive. First
every address in it was refused (rejected at SMTP time) for a
considerable period of time; then all MX records were removed for the
entire domain. After several years, he reactivated it as a spamtrap,
and almost immediately began receiving tens of thousands of messages
per day. So three years of non-deliverability did not cause those
addresses to be properly validated or invalidated.
Working at an ISP I have also seen the effects of spam runs headed
for customer mailservers "downstream" who maintain this strategy. If
they don't accept everything at SMTP time, our backup MX has to do the
same. One customer with a MS Exchange server was following this
approach; when a major spam run hit them one weekend, their mailserver
fell right over, and we ended up with 20K spams queued for non-existent
addresses in their domain over the course of a couple hours.
This is pretty clear proof that the vast majority of spammers never
winnow their address lists. If you accept all addresses, you will just
end up with more junk to deal with.
-- Clifton
--
Clifton Royston -- [EMAIL PROTECTED]
Tiki Technologies Lead Programmer/Software Architect
"My own personal theory is that this is the very dawn of the world.
We're hardly more than an eyeblink away from the fall of Troy, and
scarcely an interglaciation removed from the Altamira cave painters. We
live in extremely interesting ancient times.
I like this idea. It encourages us to be earnest and ingenious and
brave, as befits ancestral peoples; but keeps us from deciding that
because we don't know all the answers, they must be unknowable and thus
unprofitable to pursue." -- Teresa Nielsen Hayden, 1995
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