No subject

adjust and learn to retry, it is having an enormous impact on the amount of
spam delivered to the server. And it lowers bandwidth use by stopping it
even before the subject is received (let alone the message body).

By using RBL checks before greylisting, we reject with a permanent error
based on the conservative RBLs which stops retries. Then greylisting knocks
out a big percentage. Following that, we check for valid domain, valid
recipient mailbox present, and a couple of small things, then queue for
delivery. We check for viruses and malware as it is delivered to the
mailbox.

This strategy has reduce my spam intake from about 400 per day to 10 per day
and our customers are reporting similar experiences. I can live with the
trickle that's left and it does not seem to reject any legitimate mail.

Of course, we can not be 100% sure of the "no false positive" statement
because there could be mail rejected that never gets reported to us. But we
have been using the RBLs for about 4 years now and not even a suspicion of a
lost email. But the RBL must be chosen wisely.

So would I bother with my own spam trap? Probably not.

Cheers
Graham