Preview text, sometimes known as the preheader, is the snippet of text that appears after the email subject line in most email programs. (The combination of from, subject line and preview text is reminiscent of the Johnson Box used in direct mail.) It is a feature that email marketers can use to improve their delivery rates, by improving how their message looks in the inbox. It's often overlooked in message creation. If you do not create it in your message, email clients will display the first line of text in your message in its place.
How long should it be?
Most email clients display 35-90 characters of preview text, although Apple Mail displays 140 and some email clients, like older versions of Outlook, don’t display any. Keep the email clients your customers use in mind when determining how long your preview text should be. If you only send one version of your email message you may want to write over 100 characters, with the understanding that not everyone will see the entire version.
Should preview text be seen in your message?
Email clients use the beginning of email messages as preview text. In some cases this leads to alt tags and menus being displayed. In these cases the email client is showing something in the inbox that was probably never meant to be seen!
A preheader can prevent email clients from pulling alt text or navigation bars as preview text. A preheader is copy that goes at the very top of your email message. It acts as both a visible header in the body of your email and preview text.
Invisible Preview Text
The alternative to a visible preheader is invisible preview text. This text is displayed properly by email clients, but it’s invisible to anyone looking at the email body. Creating it can be a bit tricky, but below is an example of the code that can be used.
A quick and easy hack for creating invisible preview text is to use very small font to type it at the very top of my message and change the font color to the background color. It’s the simplest solution and it works for anyone who doesn’t want to edit their source code directly. It's important to note that this could trigger a spam filter, so proceed with caution if you have poor delivery rates.
Preview text tips and tricks
Front load your preview text with the most important information you want to convey. Because the display length varies between email clients, this ensures that the largest number of people possible will see your most relevant info.
Use personalization for a personal touch. Just like personalized subject lines and content, this will improve interaction rates.
Sum up your message or use your CTA in the preview text. This is not the time to reserve information for the body of your message, your goal should be to stand out in the inbox. Sharing a compelling offer might be the thing that gets your message opened.
If you can, find a way to make the subject line and preview text work together. Because they usually appear in order it makes sense to have them work in conjunction.