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How is Spam Filtered with a Mail Proxy?
Nearly all standalone spam filtering utilities are mail proxies. In the simplest possible terms, a mail proxy is a software utility that is inserted between your mail client and your mail server to process your e-mail before it is delivered to your inbox. You may not even know that a proxy is in use; all you know is that some email goes directly into a Spam or Junk Email folder.
Mail proxies can be used for various purposes, but nearly all are used to filter spam. This filtering can be done in several ways, and many filtering utilities use several different methods to separate spam from legitimate e-mail, including whitelists, blacklists, keyword and key phrase filters, and statistical analysis.
Typically, a mail proxy will look at a message in the light of its various filtering technologies and then decide whether it’s spam or legitimate. The mail proxy will then mark the message somehow, often by inserting a short tag at the beginning of the subject line, and then send it down to the e-mail client.
The e-mail client still has a part in the filtering task: It looks at the markers added by the mail proxy and routes anything marked as spam to its trash folder and anything marked as legitimate e-mail to its inbox.
The mail server is somewhere on the Internet, typically owned and operated by your Internet service provider (ISP). The mail proxy and e-mail client are both programs that run on your PC, which is represented by the shaded box. When your e-mail client sends out its request for new mail, this request (which usually goes directly to the server) passes through the mail proxy. The mail proxy passes on the request for new e-mail to the server, which delivers new e-mail to the proxy. The proxy inspects and marks the new e-mail and then passes it on down to the e-mail client.
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What does the computer see?
From the perspective of the e-mail client, the proxy looks like an e-mail server. The proxy accepts requests for new mail and sends mail back to the client. From the perspective of the e-mail server, the proxy looks like an e-mail client. The proxy sends the server a username and password and accepts the mail that the server sends back. This allows both the client and the server to operate pretty much as they always did, when they only spoke to one another, without the mail proxy in between.
A mail proxy must be configured with your e-mail account information because it acts as an e-mail client “by proxy" when communicating with your e-mail server. How this is done varies by product, so follow the installer wizard or other documentation for the product that you choose.
The image in this article is from the author's computer, from Microsoft Outlook 2010.
If you'd like a no-cost solution to controlling Spam on only a few computers, consider this article: No Cost Solutions to Stop Spam.
If you want to help stop spam, you can report it. Read Reporting Spam for more information.