Sendmail: How does one blacklist annoying spammers?

[Greg Woods]

On Sat, 2010-06-26 at 22:47 +0800, Ed Greshko wrote:

> A while back I did some observations and found that greylisting was most
> effective at cutting spam. 

I forgot to mention that we use greylisting too; I highly recommend this
as well. It is difficult to tell how many greylisted messages were spams
that never came in and how many were legit messages that were later
retried. Messages that get blocked by a DNSBL never get far enough to be
greylisted either (no point since we already know it's spam, why invite
them to retry?)

It should be noted that greylisting *will* cause some delays in
legitimate messages, and the length of the delay is totally under the
control of the sending server. Personally, I think any communication
that can't tolerate a few minutes or even an hour delay should be sent
by some medium other than e-mail (instant messaging, even a phone call),
but that said, I do get a lot of complaints about delays caused by
greylisting, so this should be borne in mind. Most people shut up when I
offer to turn if off for them so they can instantly receive all their
spam :-)

--Greg