Milter-greylist

Very few spammers still used dedicated systems to send out their wares, most now use bot farms.

This means that they will be sending via real MTAs, which will retry.

Looking at my logs over the last two days I see this:

# grep "Greylisting in action" mail | wc -l
1234
# grep "delayed for" mail | wc -l
1234

So every email delayed by greylisting was eventually re-sent and accepted.

Most SPAM was blocked by RBLs, that which passed (the 1234 above) then went on to SpamAssassin, which trashed around 1,210 of them as SPAM.

Greylisting contributed ... zero.