---
title: How spam filters work
description: 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.
---

# How spam filters work

 Written by ** [ Nathan Thomas ](https://blogs.alamode.com/qa-blog/author/nathan-thomas) ** on **June 8, 2005**

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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.

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