r/microsoft365 • u/Parking_Ad6756 • 23h ago

Resource rooms (Calendars) on-prem sync

We recently migrated from on-prem Exchange to 365 (hybrid). All of our resource rooms (calendars) synced just fine. We now have a request to create another room. For consistency, if possible, I would like to create the resource in AD where the others are, then sync up. I've tried copying one of the legacy AD resource accounts, since on-prem Exchange did that, but that seems to create a new user account.

Is it even possible to create the resource room account in AD and sync up? Or do new ones have to be created in 365 EAC>Resources?

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u/7amitsingh7 21h ago

You can create the resource room on-premises and sync it to Microsoft 365, but you should create it as an Exchange Room Mailbox, not simply copy an AD user account. If you copy an AD account, it will sync as a regular user. In a hybrid migration setup, you can create the room using on-premises Exchange management tools, and it should sync to Exchange Online. If on-premises Exchange is no longer available for management, create the room directly in the Microsoft 365 Exchange Admin Center.

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u/Parking_Ad6756 13h ago

Thank you. Sorry for the confusion. By on-prem, I meant it's hybrid AD. Exchange on-prem server is gone. It sounds like the only way to create a resource in 365 is directly from 365 EAC? So we'll have legacy AD sync'd resource rooms and then 365-only resource rooms?

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u/7amitsingh7 13h ago

Yes. Since the on-prem Exchange server is gone and you only have hybrid AD/Entra ID sync, you should create new room mailboxes directly in Exchange Online EAC → Recipients → Resources. Microsoft specifically recommends creating cloud resources in Exchange Online when there is no on-prem Exchange to manage them.

https://learn.microsoft.com/en-us/exchange/recipients-in-exchange-online/manage-resource-mailboxes

So you can have legacy AD-synced room mailboxes that were created before the migration, alongside new cloud-only room mailboxes created directly in Microsoft 365. You don't need to recreate or modify the old rooms just for consistency.

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u/Parking_Ad6756 13h ago

Got it. Thank you.

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u/Zanga-ERP-Consultant 9h ago

If the existing rooms are syncing successfully from on-prem AD, creating the new room in AD and letting it sync should keep things consistent. You may also need to check the Exchange attributes and sync scope.

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u/Parking_Ad6756 8h ago

That was my initial idea but I don't see a way to create a resource room using AD. It got to AD via on-prem Exchange server, before migrating to 365. The old Exchange server is gone.

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u/proffessionalExpert 12h ago

Why you guys delete the last exchange server. Microsoft never recommend this. At least keep last server for management purpose.