We're coming up on the end of our email migration, from a local Exchange 2010 server to O365 Hosted Exchange. Everything on the backend is done, and users can now access their new accounts via office.com, but all the installed Outlook clients are still pointed at the on-prem Exchange. The external company handling the migration told us to manually create new mail profiles for each user account, which would take an unreasonable amount of time.

Is there a way to force them all to do this via Powershell? The best idea I can come up with is wiping the mail profiles in the registry and then letting Outlook prompt the user to sign in with their O365 credentials, but I'd like to sort it out without involving the user if possible.

Thanks for any help you can provide.