https://groups.google.com/g/google-apps-script-community/c/G4d8c-Ual_c
Watermark in email sent with MailApp.sendEmail(options) - Possible?
email sentwatermarksendemailoptionspossible
https://developers.google.com/apps-script/reference/mail/mail-app?hl=en
Class MailApp | Apps Script | Google for Developers
Learn how to use Apps Script Class MailApp. Sends email.
apps scriptclassgoogledevelopers