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We are specifically focused on throttling of Exchange Web Services (EWS) and MAPI with RPC over HTTP (as used by Microsoft Outlook) and with hard limits set by the Exchange Online system. Any mention of specific setting values were obtained for the service version 18.104.22.168. You will want to have your tenant admin obtain and confirm setting values.
Note An on-premise Microsoft Exchange deployment may have a different throttling policy. Administrators can modify throttling settings for Microsoft Exchange on-premises. Administrators cannot configure throttling policies for Exchange Online.
What is the impact of exceeding throttling budgets?
Exchange throttling is based on the amount of Active Directory, Exchange store, and other resources a client consumes. A budget is allocated to each client to limit the resources a particular user consumes. This budget is recharged every minute.
EWS clients can exceed their budgets by sending too many concurrent requests, or by requesting too many resources on the server. When this occurs, additional requests are queued until one of two things happen:
When MAPI clients exceed their budgets, additional requests are returned with an error, until the application is under budget. There is no queuing of requests.
How do I get throttling settings?
Tenant administrators can view throttling settings by using Remote PowerShell and the Get-ThrottlingPolicy cmdlet. For information about how to connect Remote PowerShell for your tenant, see Install and Configure Windows PowerShell and Connect Windows PowerShell to the Service on Microsoft TechNet.
Use the Get-ThrottlingPolicy cmdlet (without arguments) to get all the throttling policy settings. Throttling policies might change to enhance service performance, so you should confirm throttling policies. We suggest that you make your client applications configurable to adjust for potential changes in throttling policy for Exchange Online. Additionally, because Exchange Online and Exchange on-premises might have different throttling policies, you may want to account for this when you design your client applications.
What are the common throttling settings?
The following throttling settings are common to both EWS and MAPI (RPC over HTTP) clients:
What are the MAPI with RPC over HTTP throttling settings?
The prefix RCA in the MAPI RPC/HTTP settings represents RPC Client Access. The following throttling settings are specific to MAPI RPC over HTTP:
What are the Exchange Web Services throttling settings?
The following throttling settings are specific to Exchange Web Services:
For more information about EWS throttling policy, see EWS Best Practices: Understanding Throttling Policies.
What are the specific Exchange Web Services limits?
The following are the specific EWS throttling limits:
Note The values for this limit differ for an on-premise Exchange 2010 deployment. In the initial release version of Exchange 2010, the message size limit is 10 MB. In Exchange 2010 Service Pack 1 (SP1), the message size limit is 35 MB.