There are two key elements of good email subject lines. They select, from the multitude of readers, those who are interested in the subject of the report. And they promise them a worthwhile reward for reading it.

What kinds of rewards do good email subject lines promise? How important a part does the subject line alone play in the success of an email marketing campaign? Let's tackle the second question first.

How important is the subject line?

Most marketers would say that 50%, 60% and even 80% of an email marketing campaign success depends on the subject line. And they're right because without someone opening your emails, you won't get any clicks on your link; and if you don't get the click, you don't make the sale, right.

The truth is that you cannot possibly evaluate a subject line in percentage. Nobody can. One subject line could do wonders, while the other could bomb.

The BIG question is what makes the difference…

Believe it or not, the main purpose of a subject line is to attract your attention by all means - and that's to make you open the e-mail. It is not to sound funny, or sexy.

You can craft the hottest subject lines and win awards with your copy, but what counts in the end is how effective that subject line is, to get you to open the email.

Your subject line needs to capture your prospects' attention and offer a reward for reading. This reward must be sufficiently attractive to pull the reader into the message. Imagine you're holding a red flag in your hands and want to attract the right person's attention.

You could get their attention for a second, but unless you have a specific message written on the flag that makes them take action and do what you say, it's a wasted effort. So it's not enough to attract people's attention with a subject line but you should also have a specific message such as a benefit-oriented promise, or some sort of reward, so that you get the reader into reading your whole email, click the link and do what you want them to do. Imagine a subject line no different than a headline in a newspaper or a title on the cover of a book. It not only has to attract your attention but also lure you into reading further.