RE: FN-FORUM: Boxtrapper

date posted 21st November 2007 09:28

> -----Original Message-----
> Quoting Rob Owen [EMAIL REMOVED]
>
> You should look at something like SpamAssassin. Spamassassin with
> Bayesian checking turned on works wonders. I've also heard good things
> about greylisting - but I haven't tried this yet.


Graylisting is great and gets rid of a LOT of spam (90% +) before it even
reaches the standard spam filter.

What is relies on is that spam bots are generally dumb clients and don't
conform to SMTP protocols for sending emails and the fact that most spam
will be from people you don't know and who have never emailed us before and
is essentially and automated white list..

When an email is received from a non-graylisted email address it is sent a
"Server temporarily unavailable, please retry in a few mins" message, if the
sending server retries (as it should) then the spam trap knows that it is a
valid email server and adds it to the main graylist and lets the email
through.

Emails on the graylist are kept valid for a few months so subsequent email
attempts from the same address aren't subject to the "Server temporarily
unavailable" check and the timeout is reset if more emails are received from
the same email address so people who email your often are not affected.

That's a simplistic view but you get the idea I hope.

BTW It's part of SmarterMail v4 www.smartertools.com and a few other mail
server systems.

> > Once verified, your address is added to the whitelist and any queued
> > messages are delivered. Verification is required only once.
>
> That's a challenge/response system. They are quite common and
> generally disliked. Making legitimate people jump through extra hoops
> in order to email you is just rude.
>
> See the section on criticisms at
>
> http://en.wikipedia.org/wiki/Challenge-response_spam_filtering

Have to agree, I dislike challenge/response systems with a passion, please
don't use them anyone.