How to configure the new Room Finder in Outlook

UPDATE: finally! After a month of checking with Microsoft support, they showed us this link https://docs.microsoft.com/en-us/exchange/address-books/address-book-policies/address-book-policies, and the culprit was that we used a Custom Address List for Room Lists on our ABP, and that Address List filter was not based on "RecipientDisplayType -eq 'ConferenceRoomMailbox' -or RecipientDisplayType -eq 'SyncedConferenceRoomMailbox'", but rather our owns CustomAttributes that we used OnPremise.

Replacing our "CustomAttribute2 -eq 'Room' (...)" filter by this one (which is present on the default list "All Rooms") made it work.

I can't believe checking all the Google pages never led us to this or anyone else with similar issue. The_Exchange_Team might be worth indicating it in the article.

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Since this feature, nobody in our company can find the existing Rooms Lists anymore on WebMail. Everything works fine on Outlook.

• We are in Hybrid
• All Room Lists exists OnPremise, and are synced to Azure / Exchange Online
• All Meeting Rooms are OnPremise, have the fields City, Country filled, and are synced to Azure / Exchange Online
• They are all present in the Global Address List (Rooms + RoomLists)

What happens:

• We see all the Cities in the Room Finder (so it detected correctly the City fields)
• BUT every cities are empty, no Building / Room Lists appear
• And because we cannot see all the Room Lists like it was before on OnPremise, people cannot select ANY room from the Room Finder

What we tried also:

• Create Online only Room List
• Create Online only Meeting Room (and add to this List)
• Fill up that Room Set-Place data.
• BUT its been 72h and the "new" City declared still doesn't appear in the Room Finder

What is causing Room Lists to not appear at all under Cities?