How many times do you go to create a user and find that it’s already there, or at least the forwarding address is. Info@, sales@, etc. Well, in Exchange 2007 you can final all the users with a forwarding address in them to quickly isolate who already has your address. To do so, use the following command:
Get-Mailbox | Where {$_.ForwardingAddress -ne $null} | Select Name, ForwardingAddress, DeliverToMailboxAndForward