The preview text of an email can be implemented in the third step of email creation, called Write. You can find it below the subject line. Just click the Edit button, fill the Preview text field in the newly opened window and then Save changes.
The preview text of the email is a direct extension of the subject line and can definitely impact recipient engagement. If the title doesn't encourage a journalist to open your message, the preview text is your second chance. Remember to provide valuable content in this field that also corresponds with the email body every time you execute an email distribution.