opendkim : A milter-based application to provide DKIM signing and verification ( http://opendkim.org )
postgrey : Postgrey is a Postfix policy server implementing greylisting ( http://postgrey.schweikert.ch/ )
spamassassin : An extensible mail filter which can identify and tag spam ( https://spamassassin.apache.org/ )
spampd : spampd is a program to scan messages for Unsolicited Commercial E-mail content ( http://www.worlddesign.com/index.cfm/rd/mta/spampd.htm )
Add an ebuild in portage :
The ebuild is now in the portage tree.
You can also use layman : emerge layman then layman -a srcshelton
For Paludis use this rsync : rsync://gentoo.zugaina.org/srcshelton-portage
If you have a problem : ycarus(-at-)zugaina.org