Why does Microsoft Bookings say 'Mailbox not found'?

Check the mailbox first#

In the 2023 thread (14 "same question" votes), the user had Business Premium with Bookings ticked, had tried several browsers and had reassigned the licence, and still got the error. None of that addresses the mailbox, which is what the error is about. Check these in order:

1. Can the user open Outlook on the web? Have them sign in at outlook.office.com with the same account. If mail doesn't open either, the problem is the mailbox, not Bookings.
2. Look at the user in the admin center. Go to Users → Active users, select the user and open the Mail tab. The moderator in the thread pointed admins there to look for errors. Then, under Licenses and apps, confirm that both the Exchange Online service and Microsoft Bookings are ticked.
3. Check in PowerShell.

Connect-ExchangeOnline

# Is there a cloud mailbox at all?
Get-EXOMailbox -Identity user@contoso.com | Format-List RecipientTypeDetails, PrimarySmtpAddress

# MailUser here means the mailbox lives somewhere else (for example on-premises)
Get-Recipient -Identity user@contoso.com | Format-List RecipientTypeDetails

# Outlook on the web must be on
Get-CASMailbox -Identity user@contoso.com | Format-List OWAEnabled, OwaMailboxPolicy
Set-CASMailbox -Identity user@contoso.com -OWAEnabled $true

4. On-premises mailboxes. The Bookings FAQ says Bookings "is a cloud-only application" and "isn't supported in a federated or hybrid environment". The Teams admin article states the practical requirement more precisely: the mailbox must be in Exchange Online, because "on-premises Exchange Server mailboxes aren't supported". In a hybrid organization, the user can't use Bookings until their mailbox has moved to Exchange Online.
5. New users and new licences. Microsoft doesn't document how long it takes before Bookings works for a new mailbox. The moderator in the thread said that if the error lasts more than a day in a cloud-only tenant, it may be a sync problem that only support can fix with back-end tools. Open a service request from the admin center.

"Everything is green, but Bookings still doesn't work"#

A 2026 thread from a school with A3 and A5 licences describes this. The admin had followed the Microsoft Learn steps for turning on Bookings with me, and Bookings still didn't appear. The AI-generated answer on that thread told admins to check EwsEnabled and add MicrosoftOWSPersonalBookings to the EWS allow list. That advice is out of date. Microsoft retired the EWS-based controls for Bookings with me on 5 August 2026 (message center post MC1418559). The Bookings with me admin article now says access is controlled only through the OWA mailbox policy.

Work through these instead:

Some notes on reading the results:

• If BookingsMailboxCreationEnabled is False, the FAQ says users can still open Bookings as staff on an existing page. They just can't create new pages, and they'll see an error if they try.
• Microsoft says changes to the org settings "may take up to four hours" to apply. Wait that long before you retest.
• The licence list and why A1 isn't on it are covered in which licence Bookings needs. The policy commands are explained in turning Bookings off or limiting who creates pages.

If the Bookings app opens but a personal link fails, see Bookings with me link not working. If every check above passes and Bookings still fails, open a support request with the error details (the err, emsg and request ID lines), because only Microsoft can see the back-end logs. For a full tenant review, the Bookings admin checklist lists every setting in one place.

BookingsXP is independent and not affiliated with or endorsed by Microsoft.