My most recent dive into preheader text usage, detailed in Many Retailers Not Optimizing Preheader Text, revealed that two preheader elements have seen rapid growth in adoption over the past year: the preheader message and "view on mobile device" link.

As of July, the preheader message was used by 56% of major online retailers, up 43 percentage points since March 2008, which was the last time I examined preheader usage. And the "view on mobile device" link has seen its usage rise to 22% from only 2% just 16 monthly earlier.

Here's what you need to know about these two preheader text elements:

Preheader Messages

Preheader messages come in three varieties. In order of popularity, they are:           

1. The preheader message reiterates or supports the subject line. For example, an Aug. 8 email from Musician's Friend with the subject line "Musician's Friend Special Offer Extended: More Credit for Gear Trade-Ins?" used its preheader message to add that customers could get more for their trade-in if they choose store credit.

2. The preheader message promotes a secondary or tertiary message in the email. For example, a Jan. 27 Gap email that had the subject line "Our New Button-Down Shirts, Starting at $34.50?" used the preheader message to promote khakis. In this implementation, the preheader message is like an extension of the subject line.

3. The preheader message promotes a message that isn't represented elsewhere in the email. For example, a Sept. 15 email from Dick's Sporting Goods with the subject line "Take 15% Off Select Products - 2 Days Only!" used its preheader message to ask subscribers to take a survey.

To add to the power of their preheader message, 76% of retailers hyperlink it to the landing page for the primary message. Unlike the "view with images" link, preheader messages should not link to the web-hosted versions of the email.

I predicted in March 2008 that we'd see preheader messages overtake the usage of whitelisting instructions within a year. That has indeed occurred, with only 48% of retailers placing whitelisting instructions in their preheaders, down 15 percentage points since last year. I expect preheader message adoption to continue to grow rapidly.

'View on Mobile Device' Links

For retailers with tech-savvy customers, the portion of their subscribers that is reading-or more likely, screening-their email on smartphones is increasing. However, smartphones are notoriously poor at rendering emails, so it's important to give those readers a quick and easy route to a mobile-friendly, text-based version of your email. A "view on a mobile device" link accomplishes that very efficiently.

In addition to giving your mobile users a better way to at least determine whether they want to save your email for later viewing, usage of the "view on mobile device" link is an indicator of the percentage of your subscriber base that interacts with your emails on mobile devices. Knowing that might inform your decision to launch a mobile website, text alerts, an iPhone app, or other initiatives.

Are you making the most of the preheader opportunity?