A. Spam can be filtered at any point before it gets into the user's inbox, and there are many options available to you. Before the mail even enters your organization, you can clean your mail by engaging an external managed mail provider or subscribing to an anti-spam service offered by your ISP.
If you prefer to buy and install the software in your systems, then an anti-spam gateway appliance can remove or tag spam before it reaches your mail server. These appliances also offer anti-virus filtering.
A third way is to add on an anti-spam software to your mail server and filter out spam mail by moving it into special spam-mail folders for each user. This has the advantage of allowing each user to customize according to individual requirements such as maintaining their own white list of good e-mail addresses or black list of spam e-mail addresses.
And, finally, if you have a small business with only a few computers, you may choose to use a consumer anti-spam product that will filter the mail on each desktop.
Anti-spam products use different technologies to detect spam. The most popular uses a rules-based approach which works well in detecting new spam e-mail messages. Rules should also be updated automatically on a weekly or daily basis, as spammers constantly change their tactics.
Another technology which is working well is Bayesian filtering which uses a mathematical analysis to look for spam-like characteristics in the e-mail. Most spammers don't use a real sender address, so your anti-spam product should be able to detect fake mail headers. Other anti-spam technologies include challenge/response, though this can cause problems for legitimate mail, and database matching where the spam is matched against a database of known spam. This is not always successful in detecting new spam and also requires frequent and large database updates.
Our expert: Allan Bell is the Asia-Pacific marketing director for McAfee.