I promised to report on my experience with graylisting
Summary, overall spam received is 35 % down on the average for last month (August).
My first full day wih greylisting was 2007-08-31
The results for the following 11 days were 996 spams 90/day 14 leakers (=1.4 %)
This is a reduction on the 140/day average for August.
(4369 spams, 80 leakers (=1.8 %), 0 false positive(s) )
The improvement in leakage may be due to the new release of SpamAssassin 2007-08-28
I should explain that my SpamCop Mail account usage is about 40% direct to account mail (nearly all semi-dictionary spam). On the rest, half POP from a legacy account and a little forwarded from elsewhere, greylisting could have no effect.
I therefore hoped for a reduction of about 40% and got 35% because out of an expected 200 direct to spamcop spams, 26 still got through so used relays (or other servers configued to retry), proofing them against greylisting.
In other news 53 % of spam received during those 11 days had a source reportable to a Chinese ISP (since I use quick reporting I didn't realise this before - I analysed the text of the emails that quick reporting sends).