User Configuration > Administrative Templates > Microsoft Office 2016 > Manage Restricted Permissions
User
HKCU\software\policies\microsoft\office\16.0\common\drm
This policy setting controls whether Office 2016 users can assign permissions to distribution lists when using Information Rights Management. If you enable this policy setting, Office 2016 users cannot specify a distribution list as an authorized party in the Permission dialog box. If you disable or do not configure this policy setting, Office 2016 users can specify distribution lists when using Information Rights Management (IRM) to restrict access to Excel workbooks, InfoPath templates, Outlook e-mail messages, PowerPoint presentations, or Word documents.