[ Jason L Tibbitts III writes: ]
> Another thing to do is to make your input filters as strong as those
> downstream of you. (But of course you know this.) I have some play code
> to implement RBL lookups on every IP address mentioned in the Received:
> lines of a message and bounce transgressing messages to the owner.
Watch out there. I've already been bitten by someone trying that without
realizing that those of us on private networks behind firewalls may
show IP numbers that fall in the holes of the RBL. One would hope that
Received headers originating behind such firewalls are removed from
messages passing through the firewall to the outside world, but 'tain't
always so. And there's no good way to determine which Received host is
such a firewall for a given message without keeping a database of them
similar to the RBL. My life as a MLM for a moderate-sized list has been
made pure hell by the ever-growing set of over zealous mail filterers.