Preview text is a snippet of content that appears just after an email's subject line in many email apps. This content can be created automatically, generally from the first bit of content of your emails, however, you can easily edit this text when setting up your mailing.
Begin by starting a new Automated or Single Mailing campaign. You'll walk through the beginning steps of creating your campaign until you get to the Template step. This is where your preview text comes into play.
To add Preview Text, add a Hidden Text block which can be found in the Buttons, Sharing & More tab:
After dropping the Hidden Text block into your email (at the top!), you can then edit the text to your preferences:
Your text will show in the template, but will not be visible to the reader viewing the actual email.
Once your text is set, be sure to send a Test email to see how it looks and reads in various mailing agents.
Your preview text should appear immediately after your subject line here:
For single mailing campaigns, you can edit this for each campaign you send. Automated campaigns will repeat the content you add when first creating your automated campaign template, or you can remove the block to allow the preview to be pulled from the first text of your email.