[solved] Mailto links requiring Mail app instead of using the default mail app

Problem: (on iOS, iPhone, iPad)

When clicking on a mail link, it ignores the default mail app and says: ”You followed a link that require the Mail app.“

Gmail is set as default mail app (cf. Settings > Gmail > Default Mail App) and Apple's Mail app is uninstalled.

Solution:

1. Install Apple's Mail app.
2. Go to Settings > Gmail > Default Mail App and select (again) Gmail.
3. (Optional: Test if it's working.)
4. Delete the Mail app.

Origin of the problem:

I uninstalled the Mail app immediately after having installed my iOS, before having actually set Gmail as default Mail app. So it looked like it was the default from the settings but that was probably actually not really set deep down in the iOS settings.