How to List all Disconnected Exchange 2010 Mailboxes:

How to List all Disconnected Exchange 2010 Mailboxes:
The Exchange Management Shell lets us find the disconnected mailboxes in the organization.

[PS] C:\>Get-MailboxDatabase | Get-MailboxStatistics | where {$_.DisconnectReason -ne $null} | ft displayname,database,disconnectreason -auto

Disconnected mailboxes can be reconnected to an Active Directory user account. If no account exists for the person you want to reconnect a mailbox to then you would first create the account in Active Directory. Then you can reconnect the mailbox.