[Exim] Converting to v4

Ok. Almost got it. Seems for some wacky reason exim 4 doesn't want to
respect an instant failure retry rule (F,0m,0m). When I set it to a one
minute failure (F,1m,1m) it works fine. Go figure that one.

Anyway, I'm nearly there I think. However, I'm trying to configure things
for the SMTP command ETRN, but whenever I connect to the port and run etrn,
I get a message: "500 Command unrecognized". How do I configure exim to
allow etrn commands?

Thanks!
-- Dan