I wrote a
"shim" program that accepts incoming SMTP connection and
passes them on to the real MTA when it gets a valid RCPT. It was
designed to turn away bogus RCPTs very very cheaply (and it works
spectacularly well for that[%]), but it also does banner delay, DATA
delay, and early talker rejection. (Because it connects through to a
real MTA in real time, it avoids the worst of the hairy issues that
plague MTAs, like queueing and retries.)
I wrote this for work, but they've given me approval to release it (I
asked preemptively); I can put it up for FTP if there's any interest.
I would, for one, be quite interested in your implementation. I have
greet_pause implemented in sendmail, and some fairly draconian custom
rules, but it needs all the help it can get.
<AOL>Me too!</AOL>
Peace... Sridhar