Unable to add a room calendar in a meeting request "You don't have permission to send to"
Background: Hybrid Exchange ONPREM Exchange 2016/Office 365
Users are all Office 365, Room Mailboxes are ONPREM
All conference rooms work fine except one I will call it ConferenceRoom1
When I add this conference room to a meeting in Outlook, I see the MailTip: You don't have permission to send to: ConferenceRoom1
If I continue anyway and send it I receive a bounce back
Delivery has failed to these recipients or groups:
Falcone Room (ConferenceRoom1@domain.com)
Your message couldn't be delivered to the recipient because you don't have permission to send to it.
Ask the recipient's email admin to add you to the accept list for the recipient.
For more information, see DSN 5.7.129 Errors in Exchange Online and Office 365.
Diagnostic information for administrators:
Generating server: IA1PR09MB9456.namprd05.prod.outlook.com
Remote Server returned '550 5.7.129 RESOLVER.RST.RestrictedToRecipientsPermission; not authorized to send to recipient because the sender isn't on the recipient's list of senders to accept mail from'
again, only this room as issues all other rooms are fine
This is a room mailbox
Issue happens when using Outlook 2016 or 365 versions