Anti-Spam
This page presents an overview of spam technologies and links to resources. This is primarily for aspiring student Computer Systems Administrators.
Anti-Spam Technologies
We can categorize techniques to filter spam into three different categories:
- Spam filters on the MTA
- Spam filtering Appliances
- Spam filtering services
Spam Filters on the MTA
Spam filters that run on the MTA work great for small companies or individuals. There exist both for pay and open source projects. Filtering may be done in a number of ways, to broad categories include: Filter email using a proxy so that the MTA doesn't know anything about the filtering mechanism or use mechanisms within the MTA to rank email using one or more spam recognition software packages. Whether your MTA knows that filtering happens or not makes not difference to the user. How filtering happens may make a big difference. Section NetworkSecurity/Spam#FilterTechniques delves more deeply into the how, and my not be of as much interest to some sysadmins or casual users.
To see current list of email filters for MTAs see: http://spam.abuse.net.
Spam Filter Appliances
Spam filter appliances proxy email to internal servers and simplify the system administrators work. These are usually more expensive, but can handle a much larger volume of traffic. Barracuda networks, Symmantic (Brightmail), Borderware, and IronPort are a few to look at. http://www.bestantispamappliance.com/ has a nice review of several appliances, but it may be a bit dated.