I just noticed something.
We have a mailbox which we use with multiple people. But this mailbox is also used for sending out mail from software and servers (via SMTP authentication).
In order to use the mailing from software, we had to give the mailbox permissions to send out mail (send as or send on behalf of).
Now we had the following issue, the mailbox mentioned above (the system mailbox) had send on behalf permissions on the mailbox of user-A. Whenever user-A received a meeting request it also ended up in the system mailbox.
How weird is that?
As we read through the BPOS manual we see this:
Send on Behalf Of Access
Send on Behalf Of access is similar to Send As access except that when the delegate user sends mail for the mailbox owner, the From field of the message will read "Sent on behalf of mailbox owner by delegate user."
The Send on Behalf Of parameter sets delegate access for the specified mailboxes, and enables the default Microsoft Outlook settings for delegates, including default folder permissions and meeting request behavior.
So the system mailbox becomes a delegate of the user-A mailbox. And this means:
By default, when you add a delegate, the delegate has full access to your Calendar and Tasks folders. The delegate can also respond to meeting requests on your behalf.
So.. setting just the send as permission was more then enough.