[Exim] TMDA

What are people's thoughts on TMDA (www.tmda.net)
In principle it looks workable. However in a high spam
location it will triple your email traffic. (If 90% of
messages are spam with unique return addresses, then
each incomming message generates 1 additional outgoing
message, with that possibly bouncing, or sitting on the
queue.

I'm looking for stories, good an bad.
--
Sherwood Botsford
St. John's School of Alberta