With Exchange 2010 SP 1 the archive mailbox functionality is a little more usable. This means we will need to discover ways to manage and report on these mailboxes.
So, “How do you see the size of the archive mailbox?”
Use get-mailboxstatistics mailboxname –archive.
To see all of the archive mailboxes Get-Mailbox -archive | Get-MailboxStatistics -archive |fl DisplayName, Total*
I haven’t test this yet, but also found this. It’s a GUI based view of all Exchange 2010 mailboxes with mailbox sizes.
Finally, the ability to see mailbox sizes in one place!!!!!
Hope it Helps