Several new mail clients (email programs) have excellent spam filters that are efficient, accurate and easy to use. They do not delete mail that is suspected to be spam, but will move it out of your Inbox to a special junk mailbox, where you can examine and delete it later. As with any automatic filter, there will be some errors -- spam that is not marked, and valid email that is -- but the error rate is usually low, and you can look at marked email before you delete it.

Something we said on the main spam page bears repeating here:

No automated spam filtering technology is perfect. Even the best will allow some spam to get through, and/or misidentify valid email as spam. This includes ISP-wide filtering, filtering services, and filtering software on individual users' machines.

The spam filters we describe here are among the best that are available today as built-in filters; they're quite good, but they're not perfect. Don't expect your spam rate to go to zero just by using a spam filter. For the best results in reducing spam, use a combination of techniques we describe on the main spam page.

The latest thing

The hot new technology in mail client filtering is called Bayesian filtering, named after English mathematician Thomas Bayes (1702 - 1761). Bayesian filters start with certain basic built-in rules, but are then "taught" by the user as to what the user considers to be spam. Typically, the user will indicate that they regard a message as spam (with a menu command or a keystroke) and the filter will incorporate information from that message into its filtering rules. As more messages are marked by the user as spam, the filtering rules get better and better, until usually very little spam makes it to the inbox. Bayesian filters are not only convenient, but they tend to be fairly accurate, with relatively few false positives (valid email that is marked as spam) and false negatives (spam that is missed by the filter).

For mail clients that don't have Bayesian filtering built in, there is a third-party Bayesian filter called SpamSieve that works in conjunction with various mail clients. An add-on filter like SpamSieve is best suited to technically adept users.

Mail (OS X)

The mail program "Mail" that comes with OS X (10.2.6 and later) has its own built-in Bayesian filter.

When you first run Mail, it's in "training mode". In training mode, Mail marks messages in your inbox it considers to be spam, and you mark messages in your inbox that you consider to be spam (using a "Junk" button in Mail's button bar).

• New mail
  
  
  
  
• Mark mail you consider to be spam, using the Junk button
  
  
  
  
• One valid email, one marked as spam
  
  
  
  

To unmark a message, Select the message -- the Junk button becomes a Not Junk button -- and click the Not Junk button. As you mark messages as spam, the spam filter learns what you regard as spam, and builds a set of internal rules that it uses for all future emails. In training mode, Mail leaves messages it thinks are spam in the Inbox. When Mail is catching most spam, switch to "automatic mode" by going to Mail's Mail menu, then choose Junk Mail, then Automatic. In this mode, Mail uses the internal rules that it's built so far to automatically move mail that it thinks is spam to the Junk mailbox, including all currently marked messages in the inbox. For future spam that gets to your inbox, just mark it as junk with the Junk button.

In automatic mode, all messages marked as spam will go directly to the Junk mailbox, leaving your inbox relatively uncluttered. You should, however, periodically examine the Junk box to make sure that no valid email has been misidentified as spam. If you know for certain that you will only ever get valid email from a specific set of addresses (friends and family), you only have to look at the From address of each message in the Junk box. Otherwise, you may have to look at the Subject line as well.

The Mail program is free with OS X.

Eudora 6 (OS 9 & OS X)

Eudora 6.x in paid mode (see below) has a built-in Bayesian filter.

In Eudora 6, you simply mark messages in your inbox as spam, and they are moved to the Junk box. Eudora uses each message you mark as spam to build its internal rules for determining whether or not future messages are spam.

Eudora 6 is available in a free mode, which displays small ads on your monitor, but you must purchase the product (which then does not display ads) to use its spam filtering.

Outlook Express (OS 9 only)

We mention Outlook Express here for historical reasons only. Later versions of Outlook Express had a built-in spam filter, but it didn't seem to have the features required for spam filtering in today's environment.

Entourage (OS 9 & OS X)

Microsoft's Entourage appears to have essentially the same spam filter mechanism that Outlook Express did.

Entourage is purchased as part of the Microsoft Office product line.

Other mail clients

• Mailsmith - Has a Bayesian filter (you indicate which emails you regard as spam, MailSmith builds filtering rules automatically).
• PowerMail - Has a non-Bayesian filter (you build filtering rules manually).
• QuickMail Pro - Has a non-Bayesian filter.