Your email clickthrough rate shows how often individuals have clicked on one or more links in your email. This statistic is tracked by encoding each link in your email with a special code. Every email has a different special code. Since each recipient has a different code, this allows you to know which individual clicked on which links. Most mailing list companies provide this very important statistic. If yours doesn't then it's time to look for another mailing list company.

This is the single best indicator that will allow you to gauge the interest level of you marketing campaign.

Email Clickthrough Rate By Quadrant

How Do You Increase Your Clickthrough Rate?

Increasing you clickthrough rate requires planning. You need to entice the user and make them want to click on the link!

Here are a few examples. Sometimes just changing the text of a link can entice more clicks.

Instead of	Try This
Click Here to Buy Pet Food.	Learn More About Natural Pet Foods.
Buy Fresh Pizza Now!	Take a Peek at the Ingredients.
Wrinkle Cream Special.	See What Experts Say About This New Discovery.
View Our New Clothing.	View the Latest Fashions.

In the examples above you're trying to pique the readers' curiosity. I fall for this all the time. Just look at the front page of Yahoo! Every slider photo has a link that makes you want to click it.

Too Many Links Are a Bad Thing

If you have too many links in your email spam filtering software will consider your emails to be spamming. Have you ever noticed those emails with one large photo? Then underneath it in a light color text you will see a bunch of text words that's complete gibberish? The reason for this is that they are trying to decrease there text to link ratio. It's important to balance your emails with text, images, and links. You can learn more by reading "How to Avoid Spam Filters."

Source: Unlock The Inbox