so my primary microsoft/azure account is like first.last@myprimary.com
I created a new tenant, new active directory and associated it with a .com domain, like mysecondary.com
I went to configure Azure AD Connect from my mysecondary.local and it would not run with using my primary azure account to log into to azure while the configuration is running.
I created a second admin account in the new tenant, SyncUser@mysecondary.com, and everything ran just fine.
While troubleshooting why the configurator would not log in with first.last@myprimary.com I noticed the upn for that account in the Azure Active directory is:
"first.last_myprimary.com#EXT#_firstlastmyprimary.onmicroXYHMW#EXT#@mysecondary.onmicrosoft.com "
I assume that is why I couldn't login into to that azure AD.
Why is the UPN for my Azure account that crazy string in my new Azure AD?