With CU6 for Exchange 2016, Microsoft is bringing back a function that has been sorely missed. Specifically, it concerns the behavior of sent mails in shared mailboxes or proxy mailboxes.
Let's assume that the users Frank and Hans access a shared mailbox with the name Info:
In this example, Hans and Frank have full access and send-as rights for the Info mailbox.
Before CU6 there was the following behavior, user Frank sends a mail in the name of Info (send-as or send on behalf of does not matter), the sent mail therefore ends up in the "Sent items" folder. However, the mail only ends up in user Frank's "Sent items" folder and not in the Info mailbox. The user Hans, who also has access to Info, therefore has no way of knowing if, when and what Frank has replied to a mail:
Frank sends the mail on behalf of Info, the mail only ends up in Frank's mailbox in the "Sent items" folder, no mail is displayed in the "Sent items" folder in the Info mailbox, so Hans is left out and knows nothing about it.
With CU6, the "MessageCopyForSentAsEnabled" and "MessageCopyForSendOnBehalfEnabled" features have now been reintroduced. "Reintroduced" because it existed before, but was not previously included in Exchange 2016.
If the feature for the info mailbox is now activated, the following happens:
User Frank sends another mail on behalf of Info. The mail is saved in Frank's "Sent items" folder, and a copy of the mail is also saved in the "Sent items" folder in the Info mailbox:
This means that Hans can now see that user Frank has replied to an e-mail or written a new e-mail.
The new old feature can be activated with the following commands for a shared mailbox:
set-mailbox Info -MessageCopyForSendOnBehalfEnabled:$true -MessageCopyForSentAsEnabled:$true
A distinction is made here between "Send-Als" (MessageCopyForSentAsEnabled) and "Send on behalf of "MessageCopyForSendOnBehalfEnabled". The behavior can therefore be controlled for both variants.
Switching off works with the following commands:
set-mailbox Info -MessageCopyForSendOnBehalfEnabled:$false -MessageCopyForSentAsEnabled:$false
Unfortunately, it is still not possible to centrally control what should happen to deleted items. If user Frank deletes a mail in the Info mailbox, the mail is moved to the "Deleted items" folder in Frank's mailbox. Hans is once again left out when he searches for deleted mails. For "Deleted items", the behavior can still only be adjusted via registry key or group policy (Described here)