The Exchange Web Service (EWS) throttling policies ensures the reliable functioning and uptime of the Exchange Server with the help of values defined in the throttling policies.
The applications that use the EWS functions as per the values defined by these policies. If the applications exceed the defined values, then the EWS generates errors.
The throttling policy parameters that affect the applications that use the EWS are many. The EWSMaxSubscriptions is one such throttling policy parameter that affects the ENS application.
This parameter defines the maximum number of subscriptions for a service account.
You can alter the default subscription value for Exchange Server 2010 and 2013 but not for Office 365.
On the ENS configuration file, maxSubscriptionsPerConnection="200" maxConnectionsPerUser="10" are the two throttling policy parameters that match the default value of the EWSMaxSubscription parameter on the Exchange.
When the ENS makes an API call to AirWatch to fetch the user details and if the number of users fetched is greater than the values defined in the parameters, then the ENS generates the error “Insufficient service users in domain to monitor mailbox email@example.com”.
To avoid such errors, depending on the Exchange server type you can either increase the number of subscriptions for the service account or add more service accounts.
- Office 365 - You can add more service accounts using the ENS Config Tool. For information on configuring multiple service accounts, see Create Multiple Exchange Servers and Service Accounts.
- Exchange 2010 and 2013 - You can set a higher value for 'EWSMaxSubscriptions' using PowerShell commands. Every time you set the subscription value on the Exchange, you must also set the value for the throttling policy parameter 'maxConnectionsPerUser' on the ENS.