Apple Watch allows the sending of secret messages thanks to the way in which its application for displaying emails was thought, so that skilled users can send emails with content that cannot be displayed on other terminals. The "function" offered by the Apple Watch is based on a special formatting of the content using HTML code, so you have to know exactly what you are doing to be able to use this little trick and send messages that only certain people can view.
Everything is based on the fact that the Mail application for Apple Watch only displays the clear texts of messages, ignoring complex HTML codes and images, in order not to consume too much energy, so that a clear message hidden in an HTML code can be displayed. Normally, emails contain HTML code and elements in clear text whose content is determined by the Content-Type code: text / html si text/plain.
Usually the Watch displays only the plain text part of your email. This happens because of a quirk. When the Watch notices a remote image in your email, it considers the HTML too complicated, so it shows the plain text version instead. For reference, a remote image is an image that isn't embedded in the email, but instead loaded from a server using a standard tag—99% of images in emails are loaded this way. Remember, we're displaying email on a watch here, folks. It needs to be simple!
Because Apple Watch is special, he replaces the classic display method with text/watch-html in the idea of replacing complex code or unsupported HTML elements, so that only texts will be displayed, without other codes. In order to send an email compatible with what the Apple Watch displays, you will have to use a special service that allows marking the content with text/watch-html, and this is not easy to find.
If you are still interested in trying everything, you can use PutsMail and you can send emails with hidden messages to your friends, they are not visible on the mobile terminals, nor on the iPhones that process the content.
