- set up greylisting on the primary MX
- set up greylisting on the secondary MX
- configured sendmail to bounce the two top fake addresses that spammers use when faking my domain
...today's spam count in my inbox is 1. One spam. No bounces, or challenge-responses, or postmasters, or what have you.
I just checked in my gmail "spam" folder, and there are only two messages there, one of which I put there because we no longer do business with the store that sent this message.
While I am sure that things will get worse again, I'm pretty pleased that I've been able to make things a bit better so simply.