Some of the most profitable email campaigns have subject lines that have some element of scarcity. You see this with subject lines like, "It ends tonight at midnight!", "There are only 4 left", "One spot just opened up", etc.

But don't just limit yourself to an event. You can also use situations to communicate fear of loss, which inherently creates tension. For example:

* "When she learned my secrets…"

* "Unless you do this, you are lost!"

* "The sneaky mind trick they use on you"

* "You are losing money right now!"

For example, the subject line starts with "It all started when…" and in the body of the email, it goes on with "… She told me about this website!" The subject says "I've never had a chance to…" followed in the email by "… tell you about this amazing secret!" Or the subject says "Don't leave me…" continued with "… hanging by not responding to this offer." You get the picture.

The best curiosity subject lines are those that really tease not by omission but by implication. In fact, one curiosity-building tactic that works quite well is to tempt an open by implying that the answer to a question is within your email.

* "The real reason people gain weight"

* "No joke! Shocking study proves laughter is dangerous"

* "Is he cheating? Find out with these 6 tell-tale tips"

The word "controversial," by definition, means "of a diverging viewpoint," "opinionated," "disputed," "arguable," "contentious," etc. Being controversial simply means to be different.

Take a look at some of Michel's headlines that spark controversy:

* The Death of The Salesletter

* Ordering Offline Boosts Online Sales?

* Forget Benefits And You Will Sell More