Before you can remove the disconnected mailbox from Exchange 2007, you need to figure out the MailboxGuid and also the coresponding database:
Get-MailboxStatistics | where-object { $_.DisconnectDate -ne $null } | Select DisplayName,MailboxGuid
Get-Mailbox -Identity mailboxname | FL
To remove a disconnected mailbox from Exchange 2007 you can use following cmdlet:
Remove-Mailbox -StoreMailboxIdentity d6dd0587-6a62-446a-a1ef-0b785dac1090 -Database sg1mdb1
