The difference between R6 and R7 MESSAGING is the phantom and auto copy feature.
In R6, you could auto-copy ONE mail box to ONE other mailbox. In R7, you can auto-copy MULTIPLE mailboxes to ONE mailbox.
In R6, you could make ONE mailbox be the phantom receiver for ONE other mailbox. In R7, you can make ONE mailbox be the receiver for MULTIPLE mailboxes.
This doesn't mean that you can have only one auto-copy or phantom receiver, it means that every receiver can have multiple senders.