As part of this process, there are local AD user accounts that needed to be linked to Office 365 mailboxes in a way that the local Exchange implementation could understand. I've described that process here:
Here is the process I used:
- Create a disabled user account with the same name as the O365 room.
- Convert the disabled user to a mail user:
- Set the External e-mail address to be for the O365 object. This should be XX@XX.mail.onmicrosoft.com.
- Set the local domain as the reply email address. This needs to match the address in O365 because that is how Dirsync matches the disabled user account to the O365 object.
- On the E-Mail addresses tab, uncheck the Automatically update e-mail addresses based on e-mail address policy check box.
- Select the correct e-mail address XX@yourdomain.com and click Set as Reply.
- Click Apply.
- Check the Automatically update e-mail addresses based on e-mail address policy check box and click Apply.
- Use AD Users and Computers to Edit the properties of the disabled user account. Advanced Features must be enabled in the View menu.
- On the Attribute Editor tab, modify the following values to convert the disabled mail user to a remote room mailbox:
- msExchRecipientDisplayType: -2147481850
- msExchRecipientTypeDetails: 85899334592
- msExchRemoteRecipientType: 33
Finally, run Dirsync to replicate the object to O365. The object should be matched with the existing o365 room mailbox. You can now book meetings with the room from your on-premises Exchange.
The above process seemed to work well in my personal environment with an Exchange 2010 hybrid server. However, on a recent project with an Exchange 2013 hybrid server, it didn't seem to work at all.
What we did as an alternative was link the room mailbox in O365 with a disabled mail user. Then we setup the proper mailbox ID to allow mailbox moves. Then finally, we moved the room mailbox from O365 to on-premises and then back to O365. This gave a properly configured room mailbox in O365 that showed up properly in the Exchange 2013 management tools.