Since Exchange 2010 and now with Exchange 2013, Microsoft Exchange ships with throttling policies. These are designed to prevent mis-use of system resources by end users. However, they can become a bit of a pain for applications which ‘require’ this mis-use such as Enterprise Vault or Blackberry Enterprise Manager.
These applications mis-use the system in the eyes of Exchange because they do ‘too many things’. An end-user would never need dozens of MAPI session open, or tens of items/folders open at any one time. That’s what the throttling policies are trying to protect against, but unfortunately they can interfere with the usage of these type of applications.