This little number can be used to introduce smtp banner delays for
qmail. When run between tcpserver and rblsmtpd, it'll do a reverse
lookup of the connecting IP, compare that PTR to a regex, and then apply
long banner delays if there was no PTR or if the PTR matches the
"dialup" regex. The program depends on the fact that tcpserver will set
TCPREMOTEIP, and will take advantage of TCPREMOTEHOST if it's set. If
the client tries to pipeline (ram SMTP commands down our throat before
we show them an SMTP banner), RBLSMTPD is set, notifying rblsmtpd to
refuse their mail.

Homepage:
https://www.lewis.org/~jlewis/smtp-delay/
