[Cialug] Greylisting

[Aaron Porter]

On Tue, 14 Dec 2004 20:18:14 -0600, Nathan C. Smith <smith@ipmvs.com> wrote:
> This is interesting, I had been wondering how long it would be before there
> was a need to "quarantine" e-mail for some abount of time.  I had thought it
> would be necessary for viruses.  (hold the message for n units of time,
> update the virus signature, scan the message again, pass it along)
> Interesting that it might help with Spam in this way.

A distressing ammount of spam is actually being sent by trojan'ed or
zombie desktop machines. and it' s just too expensive for them to
retry delivery. Enabling greylisting (using milter-greylist for
sendmail) on my host dropped my inbound spam by just over 90% --
meaning the number of messages that SpamAssassin gets run against. It
reduced the number of spams that actually made it into my inbox by
99.58% over the last 4 months (compared to the previous 4 months with
SpamAssassin alone).

May not be representative, pre-greylisting my average spamcount was
9500/day with peaks over 15000/day.