Written by Thomas Speekenbrink
As from EWS version 3.2.141 we have created new options in the Synchronizer admin > Technical Settings. With these options throttling issues are a thing of the past.
For a detailed description on Throttling please read this article: http://devnet.superoffice.com/Technical/Blog/exchange-online-synchronizer-throttling/
It is important to know that the Throttling issues will not magically disappear when selecting all the new options in the Technical Settings of the Synchronizer admin. Each of the new options work in a different way. Turning on all options will impact synchronizer performance negatively.
Optimize for High Server load environments
Enabling this option enables monitoring of EWS Requests. When requests take longer than a certain threshold, the Synchronizer will introduce small timeouts in between requests.
Use Incremental Change Detection only
Enabling this option will force the Synchronizer to use ICS to detect updates. Each user will be checked (in sequential order) for changes through ICS. Between each user a delay of 3 seconds is introduced.
Limit number of concurrent requests
This option regulates the maximum number of concurrent requests to Exchange. By default this is set to 20, which corresponds with the default Throttling policy in newer Exchange versions (also for Office 365).
The number of concurrent requests needs to be the number set in the EWSMaxConcurrency value of the Throttling Policy. Setting it to 0 means that an unlimited number of requests may be executed (set it to 0 when no Throttling policy is active for the syncuser).
If this option is set incorrectly, Exchange will throttle the amount of connections and the synchronizer will fail because no new connections could be opened. This results in the known error: "Exchange server down?".
Recommended settings Office 365
We have experienced best performance/compatibility when enabling the "Use Incremental Change Detection only" option and setting the "Limit number of concurrent requests" to 20.