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.
Enterprise Vault's Admin Service will report issues if the throttling policy is in place against the Vault Service Account mailbox. It does this when the service starts. This is a good thing for the product to do.
Enterprise Vault also ships with a PowerShell script which will create a new, unlimited, policy, and apply it to the Vault Service Account mailbox. But sometimes this is done at too wide a level - an Exchange organisation sometimes spans many geographies and many different administration teams. So setting the policy globally like this sometimes sends shudders down the back of corporate IT teams.
A couple of useful articles exist which help a savvy administrator to create the effects of the policy change without using the script. Effectively you do the manual steps which the scripts automate. This allows you to change and customise what is happening. Here are the links:
How to create the Enterprise Vault Service Account's throttling policy manually in Exchange 2010
http://www.symantec.com/docs/TECH157927
How to create the Enterprise Vault Service Account's throttling policy manually in Exchange 2013
http://www.symantec.com/docs/TECH216009