When an unlicensed account with no mailbox tries to access another user’s mailbox or a shared mailbox, OWA returns a 500 error: OwaUserHasNoMailboxAndNoLicenseAssignedException or UserHasNoMailboxAndNoLicenseAssignedError.
Let's look at why it happens and how to get straight into the mailbox.
The error
If you inspect the OWA startup error, it looks like this:
BootResult: configuration
err: Microsoft.Exchange.Clients.Owa2.Server.Core.OwaUserHasNoMailboxAndNoLicenseAssignedException
esrc: StartupData
et: ServerError
st: 500
ehk: X-OWA-Error
emsg: UserHasNoMailboxAndNoLicenseAssignedError
It shows up with any account that has no mailbox of its own: an unlicensed administrator, but also a regular user who was given access to a shared mailbox without holding an Exchange Online license.
Why it happens
When you browse to https://outlook.office.com/mail/, OWA tries to boot the mailbox of the account you signed in with. If that account has no Exchange Online license and no mailbox, startup fails before the app is usable. You never get the chance to open another mailbox from the UI, because the UI itself cannot load.
The account is behaving exactly as expected: it has no mailbox, so there is nothing to load at the root URL.
The fix
Do not open the root OWA URL. Browse directly to the target mailbox using its SMTP address in the URL path:
https://outlook.office.com/mail/[email protected]
OWA loads the target mailbox directly and skips the "boot my own mailbox" step that was failing.
Requirements, as always, for accessing the target mailbox:
- The account you sign in with must have Full Access on the shared mailbox.
- Full Access can take a little while to propagate after you grant it.