It may not seem evident to find out which mailboxes are accessible by a particular user or group. Through EAC, there is no apparent way to do this, as giving access for a user to a (shared) mailbox can only be done through the shared mailbox and then providing the user/group access. There is no way to query a particular user/group and show a list of mailboxes that user/group has access to. Fortunately, it seems that Powershell (EMS) does provide an easier answer.

These cmdlets work in both Office365 and on-premise Exchange 2007 or newer.

List mailboxes to which a user/group has access to:

Get-Mailbox | Get-MailboxPermission -User user1

Although the cmdlet states a user name, replacing th  ...