Store.exe is using up all of our availab

We have a problem where the store.exe is using up all of our available RAM. I believe the Exchange DBA grabs as much RAM as it can and watches how the OS and other BackOffice applications use RAM and then releases chunks of RAM as other applications need it. When the other applications release some of their RAM, DBA grabs it for Exchange Server again.
Unfortunately RAM is not being released and if it was not for the Rampage tool we installed which defrags the RAM stopping all available RAM being used by store.exe, it would run out completely!
Any ideas would be appreciated.