All our mailboxes are created on our On-Premise Exchange 2019 and migrated to Exchange Online and back again to On-Premise. So they all exist on the On-Premise Exchange. They all have an Exchange Online license, and Office 365 have registred that the mailboxes exist On-Premise and did not create a Exchange Online mailbox for them. Which is all fine.
But when our users press the Outlook icon in Office 365 they are forwarded to Outlook online where they get the following error:
They are supposed to get a message that tells them that their mailboxes exist on the On-Premise server with a link to webmail. This works fine for all new users created.
Do any have an idea why it doenst work with the old users?
Our OrganizationRelationship looks fine with the correct TargetOwaURL and as said it works fine with new users.