From Heinz Tschabitscher,
Your Guide to Email.
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You may not be getting all the mail addressed to you. Server-level spam filters reduce the amount of unsolicited messages, but they can catch some wanted mail, too -- without you ever noticing.

Good Anti-Spam Filters -- Controlled by You

Nobody likes to get spam. Spam filters are one of the best solutions to take control of at least of a certain amount of the daily deluge of unrequested, unwanted email.

Spam filtering tools exist as desktop solutions for Windows, for Linux/Unix and for the Mac. Some of them, those of the Bayesian variety in particular, are pretty good.

But even the best tools make mistakes now and then by allowing spam into your Inbox or mistakenly filtering out legitimate mail.

Bad Anti-Spam Filters -- Beyond Control

In addition to anti-spam tools that you can install (and control) on your computer, many ISPs (Internet Service Providers) employ spam filtering at the server level.

This can be a blessing, but it is a highly problematic blessing if you have no control of what's going on behind the scenes because

• you don't know your ISP is filtering spam at all
• you don't know how the filters work and
• you don't know when a message is rejected.

If your desktop anti-spam tool makes a mistake, it can be spotted and corrected easily. If your ISP's spam filters kill a message you most probably will not even notice it.

Maybe you suddenly stop receiving a newsletter that showed up reliably in the past, or you sign up for another and never see an issue.

Indeed, newsletters and mailing lists are the most likely victims of overzealous anti-spam filters. They may be sent in bulk (like spam), but they are not a minor issue. Both the recipient and the sender can depend on the messages arriving at their destination.

How to Turn Bad Anti-Spam Filters into Good Ones

Server-side spam filters are great. They can save a lot of bandwidth for everybody, and they save a lot of hassle with spam for everybody. But there must be ways for individual users to control these filters.

Most importantly

• no mail must ever be deleted or rejected by server-side filters unless the user explicitly (and preferably repeatedly) requested this.

Instead, rejected messages should go to a special place where they can automatically expire after some time if they are not recovered. User access to mail marked as spam by the filters can be provided in a number of ways, including

• a separate folder for IMAP accounts,
• a separate POP account,
• a Web interface similar to Web-based email systems or
• an email interface that sends a summary of rejected messages daily.

What You Can Do

Spam filters are great, but not if they mean uncontrolled and uncontrollable censorship of incoming email messages.

Ask your ISP about their server-side filtering and how you can influence it. If they do not respond, think about switching to a service provider that takes your concerns seriously.