After your mailbox is moved to Microsoft Office 365 Dedicated/ITAR (vNext), you experience one of the following issues:
When you try to add another mailbox in Microsoft Outlook, you receive the following error message:
When you try to add a delegate in Outlook, you receive the following error message:
All mail user objects representing on-premises mailboxes should have a RecipientDisplayType object that permits them to be added as additional mailboxes and delegates. These objects are considered “ACLable.” Microsoft is currently working on a fix for this issue.
To confirm that this is the issue you're experiencing, review the object in the Outlook People Picker. To do this, follow these steps:
In the Outlook client, click File, click Info, and then click Account Settings.
Select Delegate Access.
Click Add, and then review the specific object:
If the object has a red slash on the icon, the user doesn't have the correct RecipientDisplayType set. Until the fix is fully deployed, contact Microsoft to resolve this issue.
As a workaround, add the account as an additional email account. To do this, follow these steps:
In the Outlook client, click File, click Info, click Account Settings, and then click Account Settings again..
On the E-mail tab, click New.
On the Auto Account Setup page, enter the Room mailbox name, email address, and your account password.
Click Next. AutoDiscover will find the mailbox and configure the account.