Apple watch’s rendering of email/email previews spits out all text, stripping HTMLs to their bare core, but not before alerting the Apple Watch user that it did so, making any HTML email’s text contents at least one screen scroll away.
But AppleInsider.com posts about a separate block of code that can be used to target Apple Watch with simple HTML. The caveat is that few mail servers support it. But if you roll your own mail server, this may work for you.
Thanks to an interesting quirk in the way Apple Watch handles email content, users willing to brave a little HTML code can include “hidden” versions of a message specifically formatted for the device.