dovecot-antispam : A dovecot antispam plugin supporting multiple backends ( http://wiki2.dovecot.org/Plugins/Antispam/ )
dovecot-antispam-hg : A dovecot antispam plugin supporting multiple backends ( http://wiki2.dovecot.org/Plugins/Antispam )
postwhite : Per-recipient whitelist policy server for Postfix MTA managed entirely by emails. ( http://www.bitcetera.com/products/postwhite )
Add an ebuild in portage :
The ebuild is now in the portage tree.
You can also use layman : emerge layman then layman -a bitcetera
For Paludis use this rsync : rsync://gentoo.zugaina.org/bitcetera-portage
If you have a problem : ycarus(-at-)zugaina.org