Are you trying to redirect the restore to an Exchange RSG, or just restore emails that were deleted?
1. If you're trying to restore to an RSG, here are 2 links you can go through which explain how it should be done:
http://seer.entsupport.symantec.com/docs/285753.htm <--Exchange Agent Best Practices
2. If you're just trying to restore Exchange emails etc, I'd suggest staging to disk first, as this takes a lot of the schlep work out of restoring. The first couple of steps redirect the Exchange temporary store of the IS to another location (by default set to C:\Temp)...
Let us know how it goes...