I must be missing something here. You're saying you want me to set up a null
MX for all my hosts to
prevent someone else's MTA having undeliverable mail sitting in the queue for
a week? Why would I care
about your MTA's queue? Why would this issue even be on my radar?
To get a definitive answer, you'd have to ask some of the many people who
already
implement null MX. In my case, it's partly because my own users mistype names
and the typos happen to be names that resolve in my DNS, and partly because
people
write and say "sorry, I wrote to ask where to send your $50,000 check and I just
saw that I mistyped your address a week ago."
The second example you give, stopping mail being delivered to the web server,
is actually served better
by setting up a proper MX that directs the mail to the right server. Does an
HTTP server really care
about the occasional SYN to port 25?
Well, OK. What would be the proper MX for mail sent to
ted(_at_)www(_dot_)ietf(_dot_)org ?
R's,
John