Assume that you configure MessageCopyForSentAsEnabled to True for a shared mailbox in a Microsoft Exchange Server 2013 environment. When a user sends an email from his or her mailbox by using the "Send As" permission of the shared mailbox, the sent email isn't copied to the Sent Items folder in the shared mailbox.
This issue occurs because an Authentication X-header isn't stamped on the message.
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.
Learn about the terminology that Microsoft uses to describe software updates.