Cloudmark's Immunity is another gateway product, sitting between your email server and the outside world. As such, you can install it on Linux or Windows Server (2000 & 2003). We tested the Linux version of the software, using Sendmail as the mail server.
Using a variety of methods, the spam agent gives a percentage rating to each email it sees. A score of 97 percent means that it is 97 percent certain that the email is spam; a score of three percent means the opposite. The agent is auto-updated from Cloudmark's servers.
With these ratings, you can easily build a new policy using the Administration Dashboard, which is accessible via a web browser. A policy states how you want to deal with the spam percentages. For example, you can block all messages through at 100 percent, quarantine messages at 75 percent and allow all messages through at 40 percent or below. You can also add whitelists of email addresses that are allowed through and make use of Sendmail's blacklisting.
As far as setting up your policy, you'll want to check reports to ensure that your settings are not too low or too high.
Once you have a policy in place, Immunity can learn from users and the administrators through the feedback system. This lets users send back badly classified messages so the system can adjust the way it looks at similar events in real time, without administrator or vendor intervention.
But feedback only works for those users you've authorized and isn't as easy, for example, as setting a forward email address for spam.
The system is smart enough to work out if the classification should be applied to just that user or the whole company, with very little intervention. It is an essential part of any spam system, as it needs to be tuned to your company.
Immunity is an incredibly easy anti-spam system to use and install, and will need very little management when running. But spam is all it does, so you will still need a more complex package to round it off.