Hi,
Based on my research, you may try using the following command to hide the room in GAL:
Get-Mailbox –Identity “Room Name” | Set-Mailbox –HiddenFromAddressListsEnabled $True
For detailed information, please have a look at the following link:
https://gallery.technet.microsoft.com/exchange/081840be-32eb-4a1e-bb6c-ebf0d5d62f0e
Since this forum focus more on questions related to Outlook client, if you need further assistance on this issue, I'd recommend you post your question to the Exchange forum:
https://social.technet.microsoft.com/Forums/office/en-US/home?category=exchangeserver
The reason why we recommend posting appropriately is you will get the most qualified pool of respondents, and other partners who read the forums regularly can either share
their knowledge or learn from your interaction with us. Thank you for your understanding.
Steve Fan
TechNet Community Support
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