We've enabled the functionality to allow you to include JSON-LD within a script tag in the head of HTML emails.
Within the script tag, annotations can be added as JSON-LD. These email annotations will allow Gmail to display your message as a 'Top deal' in the Promotional Tab and highlight key information:
- Deal Badge
- Discount Code
- Expiration Date
- Single Image Preview
Read Gmail's offical documentation on adding email annotations for the Promotional Tab.
You can also get more info in our guide to Promotional Emails.