You can enable it on account.microsoft.com > Account Info > Sign-in preferences > Add email > Add Alias and make it primary. Then click Change Sign-in Preferences, and only enable the alias.
You can enable it on account.microsoft.com > Account Info > Sign-in preferences > Add email > Add Alias and make it primary. Then click Change Sign-in Preferences, and only enable the alias.
I had to make my Outlook email primary again on my Microsoft account, unfortunately, because of how I use OneDrive. I send people share invitations and there are scenarios (or at least there were the last time I checked) where sending invitations from the primary account email is the only way to deliver the invite. If your external email alias is primary, they'll attempt to send an email from Outlook's servers that spoofs the alias email :/
...those will get "drive by" attacks no matter what.
Interesting that they're letting you alias it back to "coolkid5674321" again...
With the alias I no longer have this issue.