I am trying to set up an exchange mailbox backup job with Vembu Storegrid and StoreGrid is unable to list the mailboxes for the client. While I was troubleshooting the issue, I did notice another thing: running the Get-Mailbox command on the mail server as the backup user only shows the mailbox for that account, while running Get-Mailbox as my admin account returns a list of what appears to be all the mailboxes. My service account is a member of "Administrators", "Domain Admins", and "Domain Users". What additional permissions might be required to list all mailboxes in the system?
SnapOverflow
If the documentation for the product doesn't suggest anything better, Exchange 2010 creates an Active Directory Security Group called View-Only Organization Management which you can try adding your service account to.
Members of this group can view the properties of all objects in your Exchange 2010 environment, so can list all the mailboxes on a given server.
For reference, here's a list of all the built-in role groups in Exchange 2010.