The smtpd daemon talks the Simple Mail Transfer Protocol (SMTP) with other
SMTP daemons to receive mail from them, and saves it into a spool directory
for later processing.  It is the store portion of an SMTP store and forward
proxy.  The symbiotic companion program smtpfwdd is used to forward the
spooled mail on to its eventual destination. 

smtpd is invoked from a super-server such as inetd or juniperd. 

There is a patch available to do MAPS RBL style lookups at
ftp://ftp.obtuse.com/pub/smtpd/patch-smtpd-2.0-RBL.gz. 

Documentation is avaialble online with the juniper documentation.
See the docs for smtpd as a starting point, at
http://www.obtuse.com/juniper-docs/man/smtpd.html

Access control rules based on the connecting host, and the smtp envelope are
supported.  It contains some powerful features for stopping inbound or
outbound SPAM. 

WWW: http://www.obtuse.com/smtpd.html