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Spam 201 – Filtering out spam (junk e-mail) 

Last month I described how to keep spammers from learning about your e-mail address in the first place. If you missed it, you might want to read it first, at Spam101.aspx.

Now I'll describe how to filter out the spam that you probably already receive, so that you can concentrate on your legitimate e-mail messages.

The idea is simple really. Sometime between when a spam message leaves the spammer's Outbox and arrives in your Inbox, a filter screens it out. There are essentially two places that this can occur: 1.) at your e-mail server on the Internet, or 2.) on your local personal computer.

Filtering at the e-mail server

If you have an e-mail account, you have an e-mail server (somewhere). E-mail servers are the computers on the Internet that send and receive e-mail messages. When someone sends you an e-mail message, the Internet knows how to automatically route that message from the sender's e-mail server to your e-mail server.

Unless you work at a fairly large company that has its own e-mail server (meaning a local computer that's been set up by your company's Network Administrator), you're using a hosting company's e-mail server.

Regardless of whose e-mail server you use, it should have some spam-filtering capabilities. How well the filtering works and how flexible it is will vary greatly from one hosting company to another. The better companies will offer you choices such as how picky the filter should be and what it does with the suspected spam (does it automatically delete it forever, or move it to a temporary location in case you need to look at a suspected-spam message after all?)

If you use a web browser to check your e-mail this is the only kind of filtering you can use. That's because the e-mail is never actually downloaded from the e-mail server to your local computer, so the filtering has to occur at the server. (If you click the blue "E" in Windows to check your e-mail you're using the Internet Explorer web browser). This is how the free e-mail accounts from Yahoo and Hotmail work.

Filtering at your computer

However, if you do not use a web browser to check e-mail, but instead use an e-mail program such as Outlook to download e-mail from the server to your local computer, then you can also filter out spam as it arrives at your computer. Most e-mail programs have spam-filtering capabilities of some kind built into them. How well these filters work varies greatly, however. Some are very rudimentary, allowing much of the spam to arrive undetected. Some of the more recent versions of e-mail programs, such as Outlook 2003 on Windows and Apple's Mac OS X Mail, have sophisticated filters that work quite well.

Additionally, you can purchase third-party spam-filtering programs that run on your computer all the time, much like an anti-virus program. Some completely replace your existing e-mail program, while others work in conjunction with your existing e-mail program as a "plug-in." 

Beware the "False Positives"

The problem with any filter is the potential for the occasional "false positive." A false positive is a legitimate e-mail message that's mistakenly been identified as spam. Murphy's law seems to be alive and well in that false positives seem to mainly occur with the most important e-mail messages.

If you make a filter too restrictive you'll have a lot of false positives (and a lot of upset people asking why you didn't answer their e-mail). Loosen up the filter too much and you'll have too much spam again. The trick is to balance tightening up the filter enough to block most spam without also creating a lot of false positives.

What to do with the filtered messages?

So you've got a filter running either at the e-mail server or on your computer (or perhaps both!). Now what do you do with the messages that have been identified as spam? The obvious and emotionally satisfying answer is to just delete them.

Don't do it though. You will have false positives and you don't want them deleted. Instead, mark the suspected spam in some fashion. Perhaps they should automatically be moved to a "Suspected Spam" folder in your e-mail program. Another idea is to mark them with a color that conveys low priority, such as grey. Some filters use an icon to them to indicate that they're suspicious (MSN's web-based e-mail places a question mark in front of them).

Our favorite solution

Before we turned on spam filtering at ZolMedia.com, we were receiving hundreds of spam messages every day. As I'm sure you know wading through the spam to find the real e-mail messages was extremely frustrating.

Now that we've turned on spam filtering at our e-mail server and set Outlook 2003's built-in filtering to "high," that's no longer a problem. Almost all of the messages that arrive in our regular e-mail accounts are legit.

Here's what we do. We use a third-party e-mail host that has substantial filtering capabilities. We've tightened up the filter so that any e-mail message that's the slightest bit suspicious is forwarded to a different e-mail address – one that's dedicated to just receiving suspected spam.

When we're in the office we download e-mail for our regular e-mail accounts, as well as for our "suspected spam" e-mail account.

The regular e-mail is delivered to our Inbox. But the e-mail that arrives through the "suspected spam" e-mail account is downloaded into a different folder (named, accordingly, "Suspected Spam"). Meaning that it doesn't clutter up our Inboxes.

Then, about once a day, we quickly scan the "Suspected Spam" folder for any false positives (looking for e-mail addresses or subjects that we recognize), then delete all the spam messages.

Hide and Filter

Remember, to avoid being overwhelmed by spam, do two things. Number one, hide your e-mail address from those nefarious spammers (as described in last month's column). And number two, filter out most of the spam, being aware to look for the occasional false positive.

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