When prospects get your e-mail marketing message, they make a quick decision, usually in a couple of seconds, to open or delete it based largely on the subject line. But given the glut of promotional e-mail today, how can you convince a busy prospect — in just a few words — that your message is worthy of attention?

The “4 U’s” copywriting formula — which stands for urgent, unique, ultra-specific, and useful — can help.

Originally developed by my colleague Michael Masterson for writing more powerful headlines, the 4 U’s formula works especially well with e-mail subject lines. I’ll share it with you now.

According to this formula, strong subject lines are:

• Urgent. Urgency gives the reader a reason to act now instead of later. You can create a sense of urgency in your subject line by incorporating a time element. For instance, “Make $100,000 working from home this year” has a greater sense of urgency than “Make $100,000 working from home.” A sense of urgency can also be created with a time-limited special offer, such as a discount or premium if you order by a certain date.
• Unique. The powerful subject line either says something new, or if it says something the reader has heard before, says it in a new and fresh way. For example, “Why Japanese women have beautiful skin” was the subject line in an e-mail promoting a Japanese bath kit. This is different than the typical “Save 10% on Japanese Bath Kits.”
• Ultra-specific. Boardroom is the absolute master of ultra-specific bullets, known as “fascinations,” that tease the reader into reading further and ordering the product. Examples: “What never to eat on an airplane,” “Bill’s it’s okay to pay late,” and “Best time to file for a tax refund.” They use such fascinations in direct mail as envelope teasers and in e-mail as subject lines.
• Useful. The strong subject line appeals to the reader’s self-interest by offering a benefit. In the subject line “An Invitation to Ski & Save,” the benefit is saving money.

When you have written your subject line, ask yourself how strong it is in each of these 4 U’s. Use a scale of 1 to 4 (1 = weak, 4 = strong) to rank it in each category.

Rarely will a subject line rate a 3 or 4 on all four U’s. But if your subject line doesn’t rate a 3 or 4 on at least three of the U’s, it’s probably not as strong as it could be — and can benefit from some rewriting.

A common mistake is to defend a weak subject line by pointing to a good response. A better way to think is as follows: If the e-mail generated a profitable response despite a weak subject line, imagine how much more money you could have made by applying the 4 U’s.

A software marketer wrote to tell me he had sent out a successful e-mail marketing campaign with the subject line “Free White Paper.” How does this stack up against the 4 U’s?

• Urgent. There is no urgency or sense of timeliness. On a scale of 1 to 4, with 4 being the highest rating, “Free White Paper” is a 1.
• Unique. Not every software marketer offers a free white paper, but a lot of them do. So “Free White Paper” rates only a 2 in terms of uniqueness.
• Ultra-specific. Could the marketer have been less specific than “Free White Paper”? Yes, he could have just said “free bonus gift.” So we rate “Free White Paper” a 2 instead of a 1.
• Useful. I suppose the reader is smart enough to figure the white paper contains some helpful information he can use. On the other hand, the usefulness is in the specific information contained in the paper, which isn’t even hinted at in the headline. And does the recipient, who already has too much to read, really need yet another “Free White Paper”? I rate it a 2. Specifying the topic would help, e.g., “Free White Paper shows how to cut training costs up to 90% with e-learning.”

I urge you to go through this exercise with every e-mail subject line you write. You can also apply the formula to other copy, both online and offline, including direct mail envelope teasers, ad headlines, letter leads, Web page headlines, subheads, and bullets.

Rate the line you’ve written in all four U’s. Then rewrite it so you can upgrade your rating on at least 2 and preferably 3 or 4 of the categories by at least 1. This simple exercise may increase readership and response rates substantially for very little effort.