Watch: Third-Party Email App that Renders HTML Since Gmail as a service does not support push on iOS Mail, I do not get notifications for emails as they come in unless I use a third-party email app. I have used Outlook for iOS for a long time now, and it has worked great. However, I recently got an Apple Watch, and I was disappointed to find that the Watch app for Outlook does not render HTML in emails. The emails are plain text only.

From what I have seen so far, the built-in Mail app on Apple Watch does a good job of rendering HTML emails. I have not had any luck finding a third-party app that can do this, though, so that I can get both HTML rendering and push notifications for email. 

Do any Watch apps that render HTML emails exist, or does Apple not allow third-party email apps to render HTML for some reason?
The Apple Watch OS (watchOS) does permit rendering HTML email.  However, the Watch app must be built using watchOS 5 and use Webkit for the email.  It's also a poor experience to try to read html-formatted email on a small Watch screen.

Needless to say, most developers have not updated Watch apps specifically for this purpose and some might not ever do such an update.  

Because watchOS 5 is so new, it might take a while for developer to create such an app.  Keep checking the Watch App Store and your favorite app review sites to see if any are available or featured.