Start with the “Markdown Mail” section of the mail integration guide. That sound like basically what you want and works out of the box on iOS, and with the help of the Mail Assistant app on Mac (linked with example actions in this article:
Start with the “Markdown Mail” section of the mail integration guide. That sound like basically what you want and works out of the box on iOS, and with the help of the Mail Assistant app on Mac (linked with example actions in this article: