Mail filters are invaluable for deleting repeating spam, or identical spam e-mails that arrive multiple times, week after week.
Most e-mail programs, like GroupWise and Outlook, allow the user to set up mail filters (mail rules in GroupWise). A mail filter checks every incoming e-mail to see if it matches certain criteria defined by the user. If there’s a match, the filter takes some action on the message — usually deletion. For example, a mail filter could delete any e-mail whose Subject line contains the phrase “make money fast”.
Mail filters are most effective when matching on Subject lines. For example, if the Subject line contains “make money fast,” it’s almost certainly a derivation of the same “make money fast” spam that users have received for years. The only drawback of mail filters is that they might delete a non-spam message that happens to match the filter criteria. This is unlikely to happen, as long as filters are set up conservatively enough. Matching on “make money fast” is conservative, for example, since it’s highly unlikely that any legitimate e-mail would contain those words. On the other hand, setting up a filter to match just the word “money” in the Subject would be far too liberal.
The downside of being conservative, causing you to delete a few more spam messages by hand, is much better than the downside of being too liberal, filtering a legitimate e-mail into the trash. So be conservative.
The best filtering strategy, in fact, is a two-tiered approach:
- Tier 1: E-mails that are definitely spam are immediately deleted by the filter.
- Tier 2: E-mails that are probably spam are moved by another filter into “purgatory”, a mail folder that holds suspected spam for the user to verify and delete later.
Spammers constantly change the wording of their spams (in Subject lines and in the message body) in order to outsmart mail filters. This means that mail filters will never catch every spam. In fact, filters are only effective at all if the user is vigilant in keeping the match criteria updated with the latest wordings of the spam coming into the inbox.
Here are three suggestions for using mail filters:
- Set up mail filters to delete any spam received on multiple occasions. (Don’t create a mail filter for a spam received only once, since it may never appear again. Only create mail filters for those spams that are likely to appear again.)
- Continually create new mail filters to combat the new spams that constantly appear. (The “make money fast” spam, for example, might reappear next week as “make fast cash”).
- Do not rely exclusively on mail filters to delete spam. As described above, there will always be some spam left over to be deleted manually.
Most importantly, start off by creating a few main filters that will catch 80% of your current spam load. Here are the four that will do most of the work:
- Ignore (i.e. don’t filter or act on) any mail that is from someone in your address book.
- Filter to “purgatory” (a mail folder for suspected spam mails) any e-mail containing the letters “<html>”.. i.e. filter out any HTML mail from unknown senders. All known senders should be in your address book.
- Filter to “purgatory” any e-mail with six consecutive space characters, or three consecutive ! characters, in the Subject line.
- Automatically delete any e-mail containing any of the various vulgar words that you expect to see in sexually explicit spam.
As you add more filters, your spam filters’ accuracy will climb over 90%. Please see the section, More Spam Filters, for additional information on filters. To learn how to create rules to filter message in Microsoft Outlook, see the section Use Rules to Manage your Mail. If you would like to use any of our fore mentioned filters, please see the Downloadable Filters section.
