Mailspring/app/internal_packages/composer-templates/README.md

Composer Templates

Create templates you can use to pre-fill the N1 composer - never type the same email again! Templates live in the templates folder inside the Mailspring config folder.

Each template is an HTML file - the name of the file is the name of the template, and it's contents are the default message body.

If you include HTML <code> tags in your template, you can create regions that you can jump between and fill easily. Give <code> tags the var class to mark them as template regions. Add the empty class to make them dark yellow. When you send your message, <code> tags are always stripped so the recipient never sees any highlighting.

This example is a good starting point for plugins that want to extend the composer experience.