postfixadmin : Web Based Management tool for Postfix for dealing with Postfix Style Virtual Domain ( http://sourceforge.net/projects/postfixadmin/ )
web-cyradm : Web-based application that glues topnotch mailing technologies like cyrus-imap and postfix together. ( http://www.web-cyradm.org/ )
Add an ebuild in portage :
The ebuild is now in the portage tree.
You can also use layman : emerge layman then layman -a webapp-experimental
For Paludis use this rsync : rsync://gentoo.zugaina.org/webapp-experimental-portage
If you have a problem : ycarus(-at-)zugaina.org