[cap-talk] [OT] email spam (was: Re: cap-talk infrastructure problem?)

[Eric Northup]

Jonathan S. Shapiro wrote:
> The most likely explanation is that you sent the emails from an email
> address that is not subscribed. Messages sent from unsubscribed
> addresses are *silently* dropped without notice of any kind.
> 
> This is a regrettably necessary anti-spam measure. Long ago, I had
> mailman configured to refer those messages for approval, but when the
> spam bounces hit 1000 per day I gave up.
> 
> The only alternative is to bounce them back to the sender. The problem
> is that most of the reply addresses are spam (therefore invalid) and so
> this results in thousands of messages to me as administrator that "xx
> email address is not responding".

There are other alternative.  One that has worked well for the jhu ACM 
is greylisting -- a list of known non-spam (origin email addresses, 
origin email server, destination email address) tuples is maintained, 
and incoming email matching a known good tuple is processed as usual.

Incoming email not on the list is dropped before the mail server sends 
the SMTP receipt acknowledgment.  Real mail servers will attempt to 
re-send after some delay, and the mail is added to the whitelist if it 
is seen a second time.

Though this defense can be overcome, such counter-measures are not being 
used by the spam botnets yet.

-Eric