macos: change default mail app

Filing this under “Counter Intuitive Apple Decisions” section.

Unlike the web browser setting, which is controlled in System Preferences (makes sense), in order to change your default Mail application on MacOS, you need to use the Apple Mail app.

Once you know this, however, the steps are simple:

1. Open Settings (⌘+ ,)
2. Go to “General”
3. Select the desired “Default mail reader” from the drop down.