If you use some form of pre-authentication for ActiveSync requests, requests that are proxied on the Exchange 2013 servers are no longer preauthenticated when they are again handled by Exchange 2007.
This behavior causes a significant load increased on the Exchange 2007 servers. This can cause the ASP.Net request queues to fill up.
< processModel requestQueueLimit="25000" autoConfig="true" />
Article ID: 3125297 - Last Review: 5 Jan 2016 - Revision: 1