With the increase in the number of machines that are being unwittingly used for internet based attacks, it is obvious that businesses will need to have a way of finding out if any of their machines are affected. I had been looking for a while for a solution that is current and receives updates. I had found some old open source solutions, but it seemed as if the authors have gone on to other things and have abandoned the code.
Maia Mailguard is a Spamassasin front end that uses its own version of Amavisd to scan and process incoming and outgoing emails. I have tried looking for other frontends, but they do not seem to be able to match Maia, when it comes to the ease of use for end users. It is not the easiest frontend to install, but it is worth the trouble because of the end user response that I have had from it so far. Spamassassin and the RBL block lists do a good job of stopping most of the spam getting in, but end user participation is still good, for when the spammers switch their techniques.
Fusion Directory is a PHP based application that allows you to manage an LDAP directory. Each account can have features enabled or disabled, so if you want to allow a person to have acces to emails, but not to the VPN, then you can individually enable or disable the feature on their account. At the moment it does not support pagination for the users, so it can take a while to scroll through the users, if there are thousands of them, but the developers are working on this for the 1.1 version.