How to Lock-Down Office 365 and Add an Exception For Forwards

Created by Yves Lacombe, Modified on Mon, 13 Jan 2020 at 03:33 PM by Jason Carreiro

We've discovered over time that from time to time, Office365 gets confused in regards to the differentiation between an internal and external Email and will consider "External" an internal Email in the case of certain forwards.  This happens regularly with MS Exchange Meeting forward notifications.  So you need to add an exception to the hardening rule where you want to look for the header element X-MS-Exchange-MeetingForward-Message with the value of "forward".

See example below.