Hi,
In technet, regarding New-Remotemailbox cmdlet (https://technet.microsoft.com/en-us/library/ff607480(v=exchg.160).aspx)
There is a statement: The New-RemoteMailbox cmdlet creates an on-premises mail user. The mail user contains a specific attribute, which indicates that an associated mailbox in the service should be created when the user is synchronized to the service using directory synchronization.
What is that attribute. Can somebody explain that? Is that ImmutableId?