We’re launching today an SMTP border system, called mxHero. Being Zimbra partners we’ve basically tailored it to Zimbra.
At the moment it has a few interesting features that will enhance your Zimbra deployment. Beyond pretty real time statistics, admins can limit to whom users can send, receive. You can also copy, redirect or use any of the other 12 included plugins.
At the moment it is being distributed as a Virtual Appliance. It’s been tested for several months now - on more than 5000 email accounts.
It is the result of a year and a half of hard work. License is GPLv3. Enjoy and feedback!
Site here: mxHero - email better