How spam filters work

More and more people have begun to use spam filters as a way to deal with the volume of unwanted e-mail they get each day. There are several different kinds of filters. Here's how they work:

User defined filters. Available in most e-mail clients, this type of filter allows you to forward e-mail to different mailboxes depending on headers or contents. For example, you would filter e-mail from specific coworkers into a mailbox named after them. That way, you don't lose an important e-mail because it's buried among spam. You can also use this filter to forward any e-mail that look suspicious directly to your trash. To do this you need examine the spam e-mails you receive and take note of their characteristics and the words used in the subject line, etc.

Permission filters. This filter will block all e-mail that does not come from an authorized source. A person e-mailing you for the first time will usually receive an auto response explaining that they must visit a web page to validate their e-mail address before their e-mail will be delivered to you.

Header filters. This filter examines the headers of your e-mails to determine whether they're legitimate. In addition to the sender, receiver and subject line, e-mail headers also contain information about the server used to deliver that e-mail. Because most spammers do not want to be traced, they'll often put false information in the e-mail headers to prevent people from contacting them directly. A header filter can detect forged headers and prevent the email from going into your inbox.

Content filters. This filter denies any e-mail containing elements that the filter doesn't like from entering your inbox. It may filter e-mails containing certain words or e-mails with certain formatting such as all capital letters or non-standard colors. Unfortunately, this filter may filter bulk e-mail such as newsletters that might appear to be spam. You can avoid authorizing e-mail from domains you may subscribe to.

Language filters. This filter simply removes any email that is not in the language you speak. Because it only filters out foreign language spam, this is a good filter to use if you don't expect to get any e-mails in a language other than your own.