Every copywriter and journalist knows the importance of a powerful headline. The same applies for email subject lines, because as much as 40% of a recipient's decision to open an email is based on the subject as well as the sender.

Despite that, many still underestimate just how important the email subject line is. According to the best copywriters, one should spend half of the entire time it takes to write a piece of persuasive content on the email subject. So before pressing the send button for an email campaign, it is important to downright obsess over the email subject.

Ad man David Ogilvy knew the power of headlines and how the headline literally determined whether the advertisement would get read. He reportedly rewrote this famous headline for an automobile advertisement 104 times: “At 60 miles an hour, the only thing you hear in the new Rolls-Royce is the ticking of the dashboard clock.”

Master copywriter Gene Schwartz often spent an entire week on the first 50 words of a sales piece, including the headline and the opening paragraph. Those 50 words are the most important part of any persuasive writing, and writing them well takes time.

A general rule of thumb is that eight out of 10 people will read an email subject and send-from address, but only two out of 10 will read the rest. This is the secret to why the email subject determines the effectiveness and success of the entire campaign. The better the email subject, the better the odds of beating the averages and getting what's written read by a larger percentage of people.

In short, email subject lines, the first three lines (the preview pane), subheads and bullets should be useful and relevant to the reader. Those elements should convey a sense of urgency, and you should convey the idea that the main benefit of what follows is somehow unique.

Superstar copywriter Clayton Makepeace (www.makepeacetotalpackage.com) says to ask six questions before starting to write the email:

• Does the subject offer readers a reward for reading? Will they benefit?
• Can specifics be included to make the email subject more intriguing, believable and credible?
• Will the subject trigger a strongly positive, actionable emotion for the reader?
• Will the subject topic immediately resonate with prospects?
• Could the email subject benefit from the inclusion of a proposed transaction?
• Could an element of intrigue be added to drive the prospect into opening the copy?

One tip we'll add to the list: Don't over-hype and come across like a hard-press salesperson. Our job as marketers (and salespeople) is to develop a relationship with prospects over time.

Craig Stouffer is chief evangelist of email marketing company Pinpointe (www.pinpointe.com).