Written by Thomas Speekenbrink
When using the Exchange (Online) Synchronizer, you might end up with a crashing service and error messages in the logfile & Windows Eventlog.
The message you will notice is: Unable to receive folder notification events, Exchange server down?
This indicates that the Synchronizer is trying to open more connections than Exchange / Office 365 is allowing. Follow this KB article to solve this issue.
The preferred method would be to create a custom throttling policy without limitations. If your company allows for this then follow this KB article: How to disable Exchange Throttling for Exchange 2010 / 2013 / 2016 for the Exchange Synchronizer EWS
Please note that Office 365 is not included in that article. The reason behind this: Office 365 has no options or possibilities to influence the number of connections to Office 365. It is a set value, locked on 20 connections per user.
Finding the correct number of connections:
Finding the correct number of connections is a step where you need access to the Exchange server (or help from the Exchange admin).
The value must be equal to the value of EWSMaxConcurrency in the throttling policy of the sync user. That value is by default set to 20 and this is also the default value in the Synchronizer.
Setting it to 0 in the Synchronizer will mean that there is no limit. This corresponds to the behaviour of synchronizer versions prior to 3.2.141.
To get the EWSMaxConcurrency for the policy of the ‘syncuser’, execute the following Exchange Management Shell commands:
- Get-ThrottlingPolicyAssociation “domain\syncuser”
- Remember the ‘ThrottlingPolicyId’
- get-throttlingpolicy ENTER_POLICY_ID_HERE
- Check the value ‘EWSMaxConcurrency’