Rule # 1: Do be clear.

Email has greater personalization capability than any other marketing medium. This means that the subject line can get to the point much more directly than, say, in a direct mail campaign. You are mailing to this individual because they have given permission and there is some form of relationship. You know who they are and they know something about you. Don’t be shy - put the benefit right in the subject line. An Inbox client in the financial services industry had great success with the subject line, "We could turn your lunch money into $60,000." The subsequent message showed exactly how.

Rule #2: Don’t be "spammy"

Spam is such a non-starter in today’s email marketing universe; you don’t even want the suggestion of it tainting your campaigns. Which is why you should avoid subject lines like: "FREE!!! Dream vacation to Hawaii!!!" or "Double Your Income In Your Spare Time!" No matter what the message or the offer, be dignified – even a little understated. Don’t use exclamation points or consecutive capitals. Use a similar tenor and tone as if writing to a respected acquaintance whose relationship you value.

Rule #3: Do be enticing

Avoiding spam doesn’t mean boring your prospect to tears. Subject lines should be enticing. To make them so, you need to know what interests people; and to know that, you need to know them. It all gets back to email marketing’s biggest strategic advantage of personalization. When constructing your message, make sure you research your audience and know as much about them as individuals as possible. An Inboc customer in the distance learning field recently targeted academics with this subject line: "Transforming education through e-learning". Results on an acquisition campaign: 69% open rate with a 17% CTR.