Wht two email clients anyway?
One thing I don't understand is why they maintain two email clients?
As an Outlook user it annoys me no end when I click on a mail link and sometimes it tries to open Mail (which I don't have set up) when it should have opened Outlook
A much smarter (and easier for the users) approach would be to have a single mail client that based on license key turns on/off features and UX, so my base Win10 comes with Outlook (promoting the Office brand through name recognition) and when I apply my Office key all the other goodness lights up ... no redundant client and a better user experience.
(while making Outlook the default on macOS is more reliable than on Windows - I never see Mail.App unless I explicitly launch it - on iOS, Apple annoy the hell out of me by not letting me set the default mail client to something other than theirs)
As to advertising in the Mail client on Windows ... Microsoft obviously want to have their cake and eat it too ... charging for the OS and then plastering it with adverts to make the experience even worse