According to this article, Apple has removed the stationery from Apple Mail.
Apple Mail Stationery Removed. According to the release notes for the
macOS Mojave beta, Stationery, the HTML email feature that allowed
users to choose from pre-built email templates, has been removed from
I have installed the first beta of macOS Mojave and it appears that this is unfortunately true. Is there anyway to regain this functionality of Apple Mail and add stationery to Apple Mail v12.0?