Written by Thomas Speekenbrink
When you see the following message in the Synchronizer logfile this is usually caused by Exchange throttling.
"You have exceeded the available subscriptions for your account. Remove unnecessary subscriptions and try your request again."
In this article you can read some background information on Throttling.
We see the message most in Office 365 environments. For customers using O365 we recommend turning on ‘Use Incremental Change Detection only’ in synchronizers connected to Office 365 environments. Also make sure that the 'Limit number of concurrent requests' is set to 20 (this is the default setting in both the Synchronizer and the default Office 365 throttling policy).
Other options within the Synchronizer admin and how to change Throttling policies are described in detail in the previous mentioned article.