saritonin

I ran across your post while looking for a solution to the same problem. I'm adding an answer for the next person who may stumble onto the same issue, but unfortunately it's not a happy one. The protocol handler is set up to send the contents of the link to the app of your choice, but "An important caveat to note is that the browser sends the entire contents of the href attribute to your app. This includes the protocol, so you'll need to clear out that out before doing anything with the data." So it looks like it's up to Microsoft to make the web app handle stripping out the mailto: bit. source: https://mattwest.io/registering-protocol-handlers-to-intercept-special-links