I've turned up greylisting (using milter-greylist) on the geeklair.net mailserver.
This anti-spam measure should reduce the number of spam/virus emails that get delivered (so the volume of mail that needs to go through spamassassin and clamav is smaller).
The downside is that it makes mail delivery take a little longer (which could be especially annoying in the case of password-reminder or order confirmation emails). I've turned the amount of delay that milter-greylist needs way down, but the total delay is dependent on the sending mailserver.
I think the tradeoff is reasonable. As always, let me know if you notice any problems or have any concerns.
Are there any domains that you have in the auto-whitelist? Also, the milter-greylist page doesn't appear to be aware that it has been built on OS X (or they're not advertising that).
The auto whitelist is automatically created (hence the name).
Current db stats -
Summary: 88984 records, 86272 greylisted, 2712 whitelisted
The distributed conf file has some IP blocks whitelisted (because of broken MTAs), and I've whitelisted the backup MX host (since it's also running milter-greylist and peering with the primary mailserver).
Also, the website lists 'Darwin' (but I don't see anything about anyone else running it with postfix).