ladyWith VIS for Office 365,

your cloud UPN and on-premise can be different.

Non-Routable domains in UPN’s VIS for Office 365 also supports customers with either non-routable domains for a User Principal Name such as JoeUser@Optimal.local or multiple UPN suffixes. VIS for Office 365 handles this on-the-fly by translating on the out-bound synch and as the user authenticates to Office 365, with no data changes required in Active Directory.