[Exim] Idea to slow down spammers

Here's an interesting thought to help fight spam. The idea to to trap
spammers into a really slow connection taking up huge amounts of
resources on the spammers servers and basically trapping them. The idea
is to trap spammers in a really slow connection and if there were a lot
of servers doing this - it could really bog down the servers of the big
spammers.

There are various methods in Exim to look at the from address, host, etc
at connection time and refuse connections. Suppose for example we had a
blacklist of hosts and from addresses of some known spam servers.
Realize that this idea is limited to only big spam servers that are
easilly identifiable. Suppose you have a secondary MX record that points
to your slow server. So - the spammer bounces off the main MX record and
then ends up down the chain at a secondary MX record that just connects
really slow. Maybe as slow as 30 characters per second. If there's an
easy way to do this and enough people did this then it might put the
hurt to the spam senders. It also has the feature that if someone were
mistakenly listed - their mail would still make it through.

In fact - spammers might develop lists of server who trap spammers and
avoid sending spam to these servers. And I'd love to be on such a list.

This idea is rather crude but - who likes this idea?