Litmus just published a post on how you can create content that is specifically meant for the Apple Watch. The article came about after Dan Foody of Cloze discovered the existence of a special text/watch-html mime type.

Key Takeaways:

• The text/watch-html mime type allows you to craft content that is only displayed in the Apple Watch. Other email clients will ignore this special mime type.
  
  
• Apple Watch displays the subject line and pre-header in the message list view. This pre-header is still culled from the regular text/html portion of the email.
  
  
• Apple Watch will render the text/plain part of an email if the text/watch-html part does not exist. Apple Watch will not render any content when the email is opened if the email only contains a text/html part.
  
  
• You can send tests of email with the Watch-HTML mime type using Litmus’ Putsmail

Read the full article here.