Throttling in Exchange 2013

The way you control throttling changed in Exchange 2013.  If you recall, we set a different set of throttling attributes in Exchange 2010 when impersonating users.  Those attributes differ from user throttling attributes (this is a good thing for migrations!!) In Exchange 2010 there were seven throttling attributes.  In Exchange 2013, there are only TWO (again, we're focused on EWS impersonation access):

• EWSMaxConcurrency
• EWSMaxSubscriptions

To define a policy "SuThrottlingPolicy", and set it to your service account, "exsu", use the following:

 New-ThrottlingPolicy SuThrottlingPolicy -EWSMaxConcurrency $null -EWSMaxSubscriptions $null
 Set-ThrottlingPolicyAssociation -Identity exsu -ThrottlingPolicy SuThrottlingPolicy



For the inquiring minds, the following are set in Exchange 2010, but NOT used in Exchange 2013:

• EWSFastSearchTimeoutInSeconds
• EWSFindCountLimit
• EWSPercentTimeInAD
• EWSPercentTimeInCAS
• EWSPercentTimeInMailboxRPC

Here are the errors will you see in our log files if you hit the throttling limit (taken from MSDN:)

Error	Throttling policy parameter	Description
ErrorExceededConnectionCount	EWSMaxConcurrency	Indicates that there are more concurrent requests against the server than are allowed by a user's policy.
ErrorExceededSubscriptionCount	EWSMaxSubscriptions	Indicates that a user's throttling policy maximum subscription count has been exceeded.
ErrorExceededFindCountLimit	EWSFindCountLimit	Indicates that a search operation call has exceeded the total number of items that can be returned.
ErrorServerBusy	EWSPercentTimeInMailboxRPC EWSPercentTimeInCAS EWSPercentTimeInAD	Occurs when the server is busy. The BackOffMilliseconds value returned with ErrorServerBusy errors indicates to the client the amount of time it should wait until it should resubmit the request that caused the response that returned this error code.

Or, the HTTP status codes that are returned by throttling errors:

HTTP status code	Description
HTTP 503	Indicates that EWS requests are queuing with IIS. The client should delay sending additional requests until a later time.
HTTP 500	Indicates an internal server error with the ErrorServerBusy error code. This indicates that the client should delay sending additional requests until a later time. The response may contain a back off hint called BackOffMilliseconds. If present, the value of BackOffMilliseconds should be used as the duration until the client resubmits a request.
HTTP 200	Contains an EWS schema-based error response with an ErrorInternalServerError error code. An inner ErrorServerBusy error code may be present. This indicates that the client should delay sending additional requests until a later time.