Any self respecting Exchange SysAdmin will be able to tell you, that it is incredibly normal, and expected, for store.exe (Microsoft Exchange Information Store) to contionously grow in memory usage, until it uses 100% of the free RAM resources available.
This has been the case for as long as I can remember.
One of my clients is using SBS 2011, which comes with Exchange 2010.
They also heavily utilize the SQL components of SBS 2011.
The afore mentioned normal behavior of store.exe causes delays when doing basic things in SQL on the SBS 2011 server.
After a bit of searching, I found the following ADSIEDIT work around.
Connect to the Configuration Naming Context
Navigate to Configuration > Services > Microsoft Exchange > "Organisation Name" > Administrative Group > Servers > "Server Name" > InformationStore
Right click on InformationStore, select Properties and locate the both msExchESEParamCacheSizeMax and msExchESEPCacheSizeMin
I set the following, which is 1gb for min, and 4gb for max. Please note, that you must enable both Min and Max options for it to work.
Exchange 2007 uses different page sizes, and I only calculated for Exchange 2010.
Exchange 2013 and 2016 do not have SBS versions, so you won't ever need to worry about limiting their store.exe sizes.
Once you've done this, you need to restart the Microsoft Exchange Information Store, and it should stay under the 4gb limit.