You are working in a Microsoft Office 365 dedicated/ITAR environment.
This environment uses Microsoft Exchange Server 2010 or a later version.
In Microsoft Outlook, you try to add a delegate to a resource, a shared mailbox, or another user's mailbox.
In this scenario, you receive the following error message:
The Delegates settings were not saved correctly. Cannot activate send-on-behalf-of-list. You do not have sufficient permission to perform this operation on this object.
When a delegate is added in Outlook, the user is automatically granted "send on behalf" permissions. However, if you aren't the owner of the mailbox, the delegate is still created but the “send on behalf” permission isn't granted. Therefore, this error occurs.
The “send on behalf” permission isn't applied because of the new permissions model that was introduced in Exchange Server 2010.
If "send on behalf" permissions are required for the delegate, see the following KB article:
If the “send on behalf” permission isn't applied correctly, contact Microsoft O365 D/ITAR Support by online submission or by telephone.
If the delegate who is added requires folder-level permissions to the mailbox, you can still manage these permissions in Outlook or by using Windows Remote PowerShell.
You shouldn't receive the error message that is mentioned in the "Symptoms" section if you are the owner of the mailbox. If you are the owner, you should report this error to Microsoft O365 D/ITAR Support.
For more information about the permissions model in Exchange Server 2010, see the "Management role assignment policies" section in the following TechNet topic: