In the days when direct mail ruled the earth, the way in which a company's advertising message was received by its intended recipient didn't change much from one year to the next. Sure, people moved house once in a while, but the basic human dynamic of receiving, opening, and reading mail remained pretty much consistent. Then came e-mail, and all assumptions went out the window.

The manner in which your promotional e-mail gets read depends on a multitude of variables, most notably the e-mail client the reader is using, how that software is configured (including use of filters, if any), and the volume of e-mail he or she receives every day.

This is all by way of a disclaimer that any advice given on the topic of subject lines 1) should not be read as applying to all campaigns for all products to all markets, and 2) has a certain, inevitable shelf life. The technology you're using to read this e-mail may (and probably will) be radically altered a year from now. In addition, as the volume of unwanted junk e-mail continues to expand beyond control, the patience and receptiveness of people towards commercial e-mail in general will decline. We marketers will just need to adjust.

All that said, here are some of the subject line techniques that, for us, seem to be making a consistent difference in the success of e-mail campaigns:

1. Use "Free", at least as a test.

   Despite being one of the first words spam filters look for, our experience shows that "Free" continues to increase response rates. In one recent test for a software client, the subject line using "Free" ("Free Kit: <benefit statement>) outperformed the alternative ("Learn How <benefit statement>") by over 50 percent.

2. Mention the offer

   You've only got 40 characters or so to work with, so it's critical your subject line contain both 1) a compelling benefit and 2) an offer. One word is sufficient, for example: "Free Kit: Increase Application Performance by 300%". The benefit may be what attracts attention, but the offer is what gets the reader to open the message.

3. Life does not begin at 40.

   E-mail list owners vary in their treatment of longer subject lines. Some will reject your submission and force you to come up with a shorter version; others will abbreviate for you (sadly, sometimes without consulting you first). A few will send out messages with longer subject lines, but then most e-mail clients won't display subjects much longer than 40 characters. Don't take chances. Assume you've got 40 characters, including spaces, and work within that limit.

4. Be specific.

   Every day the average e-mail user receives dozens, possibly hundreds, of messages promising greater profits, higher income, complete happiness, and on and on. Follow their lead, and you'll get lost in the crowd. Instead, make your benefit as specific as possible. For example:

   Bad:		"Maximize profits in just 3 months! Free Kit"
   Better:		"Free Kit: Maximize e-commerce profits"
   Best:		"Free Kit: How Linux boosts e-com profits"

    
   One obvious, but often neglected, method for judging the potential effectiveness of your subject lines is to send yourself a couple of e-mails using them. Wait a few minutes for your inbox to collect a few more messages, then take a look. Does your subject line look frighteningly like spam? If so, fix it!

   (Many thanks to Doug Smith, esteemed creative director at Connect Direct, for his help with this month's tip.)