Remove disconnected mailboxes in Exchange 2007

Get all disconnected mailboxes

Get-MailboxStatistics | where-object { $_.DisconnectDate -ne $null } | Select DisplayName,MailboxGuid

Remove a single disconnected mailbox

Remove-Mailbox -Database -StoreMailboxIdentity -confirm:$false

Remove all disconnected mailboxes

$users = Get-MailboxStatistics | where-object { $_.DisconnectDate -ne $null } | Select DisplayName,MailboxGuid,Database

Then all disconnected mailboxes are in a variable and you run following cmdlet to remove mailboxes

$users | ForEach { Remove-Mailbox -Database $_.Database -StoreMailboxIdentity $_.MailboxGuid -confirm:$false }