sounds like you are using outlook 2007 with encryption turned on. Are you seeing red waring traingles for each 7830 current connection? first , uncheck encryption support within the outlook 2007 client and see if this provides optimizations for 7830?
the steelhead can support outlook 2007 encryption if configured in the right manner.
The documentation I find, including KB 1930, show 7830 as a MAPI Exchange port. Also, the port labels show a gap in the Riverbed port between 7820 & 7850: 7744, 7800-7801, 7810, 7820, 7850, 7860, 7870.
The Steelhead appliance and RiOS use the following TCP ports:
Data store sync port
MAPI Exchange port
Connection forwarding (neighbor) port
Used by Steelhead Mobile to communicate with the Mobile Controller.