Exchange On-presemise resource mailbox not showing in exchange online

Question

Need help with the following issue.

Recently, we deploy an Exchange hybrid, and everything working as expected but the Exchange resource mailbox (Hosted in on-premises) not showing in the exchange online.

Any Idea?

Thank You
Nur Hossain

Answer 1

Hi,

Please check if those user accounts are synced using AAD connect. For resource mailboxes i.e. room mailboxes, it will be synced as "Mail user" and not as room mailbox in exchange hybrid. It has to be migrated to the Office 365 to show as resource mailboxes. Resource mailboxes in Office365 doesn't require license and when synced from on-premise recipientTypeDetails will be set to mail user

https://learn.microsoft.com/en-us/exchange/troubleshoot/calendars/cannot-add-conference-rooms-to-meeting-in-owa
https://answers.microsoft.com/en-us/msoffice/forum/msoffice_o365admin-mso_dirservices/conference-room-mailboxes-showing-up-under/958e523c-9015-490e-a82c-a6d1bb516bdb

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Answer 2

Hi @Nur Hossain

Agree with the reply above from AshokM. Move the resource mailbox to the synced OU in AD, after the synchronization you will see the resource mailbox account list in Users->Active users and show as Synced from on-premises.

Then we can move this resource mailbox from on-premise to cloud. Detailed stsp here: Move mailboxes between on-premises and Exchange Online organizations in hybrid deployments

Exchange admin center->Recipients->Migration. Click +, Migrate to Exchange Online. Then create the migeation batch.
After the migration complete, we are able to see the migrated resource mailbox in cloud.

Also note that, we still need to manage that mailbox on-premise, or we will get the error information like below

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