Mail forwarding question

I’m running Exchange 5.5, and I need to forward mail from a number of senders (about 50) from mailbox A to mailbox B. The senders’ addresses (all external) are listed in a DL in Exchange.
I have set up rules on mailbox A to check for mail from members of this DL and forward/move/redirect it to mailbox B, but nothing works.
Any suggestions? the solution cannot be client-only