In the spirit of trying as many things as possible to defeat the spammers, I've added greylisting through postgrey to my mail server. So far it works very well, but with one notable exception:
I have one user who has another email account (on another domain/mailserver) which forwards to her. So the spammers send email to her forwarded account, it gets transmitted to her, with a 10 minute delay because of the greylisting. So I added her to the greylisting white list.
I'm concerned that some mailers (mostly list managers) won't like the greylisting service. I'm using the sender whitelist, but there's a possiblility that there are other senders that I don't know about that won't show up. We'll see.
