Exchange Online Room Mailbox Not Processing Meeting Requests

Question

Description:

Hello Microsoft Support,

We are experiencing an issue with Exchange Online Room Mailboxes in our Microsoft 365 tenant.

Environment

• Microsoft 365 Business Standard
• Microsoft 365 E3
• Exchange Online
• Room mailbox created from the Exchange Admin Center

Problem

We created a Room Mailbox named Board Meeting Room ([Moderator note: Personally Identifiable Information removed]@kefholdings.com).

The room mailbox is created successfully, but it does not function as a meeting room resource.

Symptoms

• Meeting invitations are successfully delivered to the room mailbox.
• The room never sends an Accept or Decline response.
• The meeting never appears in the room calendar.
• The room always appears available in Outlook.
• Outlook Room Finder does not show the room (expected until a Room List is created, but separate from the main issue).
• Attempting to open the room mailbox in Outlook on the Web returns:

• Outlook Desktop displays:

Verification Performed

We have verified the following:

• RecipientTypeDetails = RoomMailbox
• AutomateProcessing = AutoAccept
• AllBookInPolicy = True
• AllowConflicts = False
• BookingWindowInDays = 180
• Message Trace confirms meeting requests are Delivered to the room mailbox.
• Mailbox statistics are available using Get-EXOMailboxStatistics.
• Calendar folder exists.
• Room mailbox was deleted and recreated from the Exchange Admin Center with the same result.

PowerShell Results

Mailbox statistics:

Request

Could you please investigate whether there is a backend issue affecting this Exchange Online Room Mailbox?

Specifically, we would like Microsoft to verify:

• Exchange mailbox provisioning health
• Calendar Attendant / Resource Booking Assistant status
• Resource mailbox processing
• Mailbox Assistant functionality
• Any Exchange Online backend errors preventing automatic processing of meeting requests

The room mailbox appears to be correctly configured, but it does not process meeting invitations despite successful delivery.Description:

Answer 1

Dear @Admin Bernard,

I hope you’re having a good day. 

Thank you for providing such detailed information regarding this issue.

Based on your description, the room mailbox appears to have been created successfully, is correctly identified as a RoomMailbox, and the core booking settings appear to be configured appropriately. In addition, Message Trace confirms that meeting requests are being delivered to the mailbox successfully. This suggests that mail flow is functioning as expected and that the issue may be occurring during the calendar processing stage rather than during message delivery.

As a first step, I would recommend reviewing the complete Calendar Processing configuration by running:

Get-CalendarProcessing "Board Meeting Room" | Format-List *

Please pay particular attention to the following properties:

1. AutomateProcessing
2. ProcessExternalMeetingMessages
3. ResourceDelegates
4. ForwardRequestsToDelegates
5. TentativePendingApproval

Microsoft has documented scenarios where a room mailbox does not automatically process meeting requests if the messages are treated as external, even though they are successfully delivered to the mailbox.

Additionally, I would recommend creating a brand-new room mailbox with a different name and SMTP address for testing purposes. If the new room mailbox processes meeting requests correctly, this may indicate an issue specific to the original mailbox. If the new room mailbox exhibits the same behavior, the scope of the investigation may need to be expanded.

If, after these checks:

• Calendar Processing settings are confirmed to be correct,
• Meeting requests continue to be delivered successfully,
• A newly created room mailbox experiences the same symptoms,

Then I would suggest opening a support ticket with Microsoft. At that stage, the Exchange Online support team can investigate service-side components such as the Resource Booking Assistant, Calendar Attendant, Mailbox Assistants, and mailbox provisioning health, which are not accessible to tenant administrators.

You can raise a support ticket from Microsoft 365 Admin Center>Support>Help & Support.  

For reference:  Get support | Microsoft Docs   

Please understand that, as a community member, I do not have access to Exchange Online backend systems or internal Microsoft service logs and therefore cannot verify whether there is a service-side issue affecting this mailbox.

I hope the suggestions above help narrow down the root cause. If you need any further assistance or have additional questions, please don’t hesitate to reach out. I'm here to help. 

Wishing you the best of luck with the troubleshooting, and I look forward to hearing your findings.

Warm regards,  

---

If the answer is helpful, please select "Yes" and kindly upvote it. If you have extra questions about this answer, please click "Comment".  

Note: Please follow the steps in the forum documentation to enable email notifications if you want to receive the related email notification for this thread.