This has got to be a FAQ pretty soon...

Can anyone suggest a good way to spell "From and To are the same, and
don't look local"?

This would catch the last few spams we're still not blocking successfully.

Also, let's say I want to bounce everything as user unknown, but I don't
want to get returned bounces when the from address was illegitimate.  Is
there an obvious way to do this?  The naive "just bounce as user unknown"
gets bounces to postmaster on our attempts to bounce spam...

-s