EWS Throttling Error Message for Exchange Server 2013 Users
The following error message is related to your Microsoft Exchange Server 2013 settings.
Microsoft Exchange Server 2013 message throttling policies set bandwidth limits and restrict the number of processed messages. Throttling is enabled by default on Microsoft Exchange 2013.
To disable throttling, you must create an appropriate policy and assign it to the service account as documented in the Microsoft Technet article: Set Throttling Policy.