Ann Arbor Business to Business
Small Business and the Internet

How Not to be Spam

May 2004

By Mike Gould

I recently had to do a housecall to fix a problem for a client who complained he wasn't receiving email at home that he was receiving at work. I verified that the email was being held on the server for 10 days, so that he could check it from both places. Where was it? In his filtered junk folder. His spam filter was over-enthusiastically tagging half his email as spam and moving it all to the folder containing the viagra ads. I adjusted the filter to be a little less critical, and all was well.

But it got me thinking; how does one stay on the good side of spam filters and not suffer the fate of the above emails?

Basics of filtering
First, a recap of my article from June of 2001(Filtered Email, found at Most email programs (and many ISPs) now feature some form of spam filtering. Email comes into your ISP's mail server, a filterbot (if one is set up) gives it an inspection, moves suspect email to the spam box, and puts the rest of the email in your inbox. You then open your inbox and your email program displays your mail. If your particular program is set up for it, its own filterbot inspects the email and sends suspect messages to a junk folder.

The filterbot (techspeak for Filter Robot - a piece of embedded software) performs its job by examining the subject and content of the email. It follows a set of rules in deciding if a given message is spam: some variation of the spelling of viagra? Spam. "Enlarge your (insert body part here, uh, so to speak)"? Spam. And so on. The rules can get rather complicated in the never-ending battle between spammers and filterbots, and this is where you can have problems as my client did above. His filterbot turned a jaundiced eye on the most innocent of subjects, and condemned them all to the spam folder.

Most filterbots have controls on them, based on some sort of scoring. All incoming email is examined and given a score, based on the criteria set up in its rules. You usually don't have much control over the rules, but you usually have control over how the score is implemented. In other words, the filter may be set up to reject any mail with a score over 25 (0=obviously not spam, 100=obviously spam). If this is marking good mail as bad (a false positive), you can tell the filterbot to reject mail with a score of 30 and above. This is what I was able to adjust on my client's system.

Dodging the Filters
So back on topic (and I do have one), how do you ensure that your emails don't get dumped by your respondent's filtering system? Here are some tips:

Don't put known spam words in emails. Avoid "here are some viagra jokes", and any reference to body parts, for instance.

Always have a subject. This is basic netiquette, but is also a good practice as some spammers have been omitting this in an effort to avoid simple filterbots that only look at the subjects of email.

Avoid emails that only have a web address (URL) in them. If you want to send someone a URL, include some text describing the site. This is because the goal of most spam is to get you to go to a website where spammers can sell you something. Some filterbots fill flag such minimal messages as spam.

AVOID THE USE OF CAPITAL LETTERS IN THE SUBJECT LINE. A lot of spam that my filters catch is in all capitals, or has a lot of !!! or $$$ in it. One exclamation point - OK, many=spam. HELP NEEDED TO GET $$$ OUT OF NIGERIA... you get the picture.

Use a signature. This is also good netiquette, and since most spammers don't do this, will alert filterbots that your email is legitimate. My signature file (sigfile) is found at the bottom of all my out-going email and looks like this:
MondoDyne Web Works
(phone number here)
The Sound of One Hand Clicking...

Avoid excessive formatting if you are using HTML-based email. Spammers love to send email that shows up in Web-based email programs as gaudy brochures - blocks of color, bold headers, etc. Filterbots love to send such email to your junk folder.

When all else fails
Sometimes you will fall afoul of a filter no matter what you do. You send a message to a friend and the friend reports your email is in the junk pile. The first step is to ask the friend to add you to their whitelist. This is a listing of known non-spammers that the filters should pass automatically without filtering. If your spam filter is part of your email program, it usually adds everyone in your address book to the whitelist. If your filter is run by your ISP, you may need to send them a list of all those in your address book - contact them and find out how to do this if this is the case.

You may also be the victim of a blacklisted ISP. There are ISPs who are known to the Internet community as harboring spammers, and the community responds by blocking all email from them. If you are unlucky enough to be served by one of these, you may find your email blocked from many users, and your only recourse is to move to a different ISP.

Mike Gould is a mouse wrangler for the U of M, runs MondoDyne Web Works, is a member of, and welcomes comments addressed to

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