We have an on-premise AD syncing with our Office 365 via DirSync. When we create a new user locally in AD the user gets created in Office 365 but with the incorrect primary/SMTP address. We then have to manually edit the proxyAddresses attribute by using the ADSI Editor for that user and force a manual resync.
How do ensure the correct domain (and not the *.onmicrosoft.com) is used when new users are created in Office 365?
We checked that our domain is properly configured and set as the default domain in Office 365.