Clients like Gmail, the default Mail-App on Android, and many more display a preview under the heading which can typically contain the same amount of information and normally simply is the first human-readable words in the email. It would be great to have a setting for this preview text when setting up a campaign.

On the technical site one can manually override the preview text by prepending a e.g. div with width:1px (to avoid breaking responsiveness), overflow:hidden and display:none with the content set to the desired preview text and filled up to a length of at least 90 visible chars with a chain of zero-width non-joiners (‌‌) and non-breaking spaces ( ).(https://litmus.com/blog/the-little-known-preview-text-hack-you-may-want-to-use-in-every-email)