Shared Mailboxes in Exchange 2010

Exchange 2010 only considered "Shared Mailboxes" as an attribute tag on the mailbox that was used for easy licensing identification only (Shared Mailboxes don't require an Exchange CAL). "Shared" mailboxes are, as far as Exchange 2010 is concerned, just user mailboxes that multiple users have access to. Recent updates to Exchange 2013 and 2016 at release improved the Shared Mailbox methodology so that they were actually mailboxes that were attached to disabled user accounts. The shared mailboxes could only be access by users who were granted specific permissions on the mailboxes. That said, those versions of Exchange will still identify the mailboxes as "User Mailboxes" because they are not Public Folder Mailboxes. A user mailbox in Exchange 2010 is any mailbox that is tied to a User account in AD.

For your report, you'll have to determine which mailboxes have multiple users accessing them, then export the list of users who have been granted full access or delegate permission (or, depending on how your environment handles permissions, the discreet permissions for the mailboxes in question). If the mailbox has been tagged as a Shared Mailbox, you can look it up easier in EAS, but those mailboxes will show as if they were still User Mailboxes.