Mailto integration on Windows: "send to" for global install doesn't work after the local install

[charlag]

See #3574
See #3752

This time I logged in as non-admin user, installed the app globally and tried to set mailto handler. The app elevated (as expected) but doesn't how up as an option in Windows settings.

[charlag]

Also global install didn't work on Win 11 with admin user but works with local install.

[charlag]

I played with it a little bit and looked up how Windows find email clients. Here's what I've found:

• Windows looks for available email clients under \SOFTWARE\Clients\Mail\ registry path. It can be under HKLM (per device) or under HKCU (per user)
• Windows tracks default mail client under \SOFTWARE\Classes\mailto (again, different root for different purposes)
• Settings:
  • Windows 10 has "mail client" option
  • Windows 11 has "mailto" handler option
• If user goes to Tutanota settings and registers as mailto handler we write multiple registry keys:

  • tutanota/src/desktop/reg-templater.ts

    Lines 65 to 104 in 80abdf0

    	return [
    	{
    	root: `${r}\\SOFTWARE\\Clients\\Mail`,
    	value: client_template,
    	},
    	{
    	root: `${r}\\SOFTWARE\\CLASSES`,
    	value: {
    	mailto: mailto_template,
    	"tutanota.Mailto": mailto_template,
    	},
    	},
    	{
    	root: hkcr,
    	value: {
    	mailto: mailto_template,
    	"tutanota.Mailto": mailto_template,
    	},
    	},
    	{
    	root: `${r}\\SOFTWARE\\RegisteredApplications`,
    	value: {
    	tutanota: "SOFTWARE\\\\tutao\\\\tutanota\\\\Capabilities",
    	},
    	},
    	{
    	root: `${r}\\SOFTWARE\\Wow6432Node\\RegisteredApplications`,
    	value: {
    	tutanota: "SOFTWARE\\\\Wow6432Node\\\\tutao\\\\tutanota\\\\Capabilities",
    	},
    	},
    	{
    	root: `${r}\\SOFTWARE`,
    	value: capabilities_template,
    	},
    	{
    	root: `${r}\\SOFTWARE\\Wow6432Node`,
    	value: capabilities_template,
    	},
    	]

• We do not write or clean up these keys on install/uninstall, only through our settings

Knowing all of this, here's the scenario where MAPI breaks (but mailto still magically works). I did this with admin user but I imagine it works the same with any other one:

1. install client locally. Register as mailto.
2. uninstall client
3. install client globally. Register as mailto.
4. Try to right-click in files -> (show more options) -> send to -> mail recipient
5. See error message ("There is no email program... Create an association...")
6. Bonus: cleaning up keys under HKCU makes it work again

My proposal would actually be:

• Make sure that we always write \SOFTWARE\Clients\Mail\, either during install or during startup. There's no reason to not be listed as available email client
• Make sure we clean it up during uninstall, for our own sake
• We can still give user an option to set default email app through our settings, we will just write \SOFTWARE\Classes\mailto

[charlag]

Merged back into #3574