Message-Id: <199906060705.DAA10335@astro.cs.utk.edu>
From: Keith Moore <moore@cs.utk.edu>
To: "D. J. Bernstein" <djb@cr.yp.to>
cc: ietf@ietf.org, drums@cs.utk.edu
Subject: Re: Asinine anti-spam mechanisms 
In-reply-to: Your message of "06 Jun 1999 06:09:20 -0000."
             <19990606060920.22356.qmail@cr.yp.to> 
Date: Sun, 06 Jun 1999 03:05:20 -0400
Sender: moore@cs.utk.edu

Dan,

your messages to the drums list were presumably sent to the
moderator because the spam filter could not immediately verify 
the validity of your return address.

we have found this to be an incredibly effective heuristic for
detecting spam sent to our mailing lists, and the inconvenience
to senders of having their messages delayed (usually only a few
hours) until the moderator can read them is far outweighed
by the benefit of virtually eliminating spam from the lists.

we considered having the spam filter report tempfail to the 
MTA in cases where the sender's address could not be immediately
verified, so that the MTA could retry delivery later.  but 
when we analyzed the traffic we realized that such a policy 
would invite denial-of-service attack from spammers (who, 
experience indicates, will stoop to anything).  especially given the 
low ratio of false positives, it made more sense to have a human 
moderate the list.

so we concluded that having an effective spam filter was more 
important than having absolutely immediate delivery of messages.

Keith

p.s. we could make the filter even better by having it moderate all
messages containing the word 'asinine'  since such messages
are highly unlikely to be appropriate for ietf mailing lists.