Haven't we all learned over the years the importance and value of real estate? Well then consider your email preview pane to be no different than waterfront property. The above-the-fold mark in email is typically between 300 and 500 pixels. You want to optimize the use of this space for your audience as, on average, less than 50 percent of your email recipients will scroll below-the-fold.

The first step in optimizing the preview pane experience is to address image blocking. Consider that the majority of your email recipients are reading emails at work. And, therefore, more than 50 percent on average are using Microsoft Outlook. Next, consider that the majority of companies using this email client have the default setting to not show images in emails. This means if you are using mostly images in your emails, then their preview pane experience is extremely poor.

A best practice is to make sure that your emails have a healthy balance of 50 percent images and 50 percent text. Doing so will enable your email recipients to still have a positive end-user experience regardless of image blocking. Always verify that your primary message and call-to-action renders successfully across all major email clients, and check all links. For a best-in-class example, see the Southwest Vacations emails below.

  
Additionally, be sure to include pre-header text that includes your primary offer with a textual call-to-action link above the HTML email template. For example, in the above email, Southwest Vacations has included text that reads, "Barry, Don't miss out! We've got 5 great vacation deals for you to choose from! > Check them out." (Note the call-to-action link.) It has also leveraged the header successfully to include a promotional box on the right side that displays text regardless of image rendering, so its call-to-action always appears.

Consider that a growing six percent of email recipients are now reading and sending emails from mobile devices. Regardless of whether I'm receiving Southwest's email on my iPhone, Blackberry or Treo, or if I'm viewing it on Microsoft Outlook's horizontal preview pane (as shown in screen shot below), the pre-header text is the first thing I read or notice on the email.

 
The key is to make sure you always include your brand or company name, the primary call-to-action and a clickable textual link to optimize the preview pane experience.