esnail is a small SMTP trap i built last fall (long before openbsd's spamd).
it understands SMTP input on stdin and stdout and logs inputs to stderr.
it can be combined with inetd and pf or honeyd and used to observe spammers
or SMTP attacks. it logs in a format suitable for piping to an SMTP deamon
for final processing and delivery.
esnail is available under a BSD license.