If you have a contact in exchange and you want to forward a mailbox to it. Then you can use the following command to do this.
Set-Mailbox -ForwardingAddress 'blackforce.local/MyBusiness/Users/SBSUsers/ContactName' -DeliverToMailboxAndForward $true -Identity 'blackforce.local/MyBusiness/Users/SBSUsers/UserName'
The bit before the username is the OU path to the user and contact.