When an Exchange organization is created, a default throttling policy is automatically created that implicitly governs all users within that organization. Although the default client throttling policy is generally sufficient to manage the load placed on your Exchange system, you can customize the default policy or add additional policies based on the needs of your organization.

If you’re hosting multiple tenants in your Exchange organization, you can define an acceptable load for each user of a tenant. Similarly, if you’re an on-premise organization, you can define an acceptable load on a user-by-user basis. Through policies, Exchange evaluates how each user uses the system and ensures that the resulting per-user load falls within acceptable boundaries as defined by the user’s policy. The client throttling system tracks system usage on a per-user basis and uses the throttling policy associated with that user to determine if throttling should occur.

So basically if you have multiple departments and you want to seggregate how many emails users in each department can send or how frequently they want to send it then Client Throttling policies can be created based on that,With Exchange 2010 we can limit the number of messages a user sends, using the RecipientRateLimit and MessageRateLimit parameters in a Throttling Policy.

 MessageRateLimit

It Controls the number of messages per minute that can be submitted. When messages are submitted using Outlook or OWA, the messages will stay in the Outbox longer when the user submits messages at a rate greater than the MessageRateLimit parameter. The messages are deferred, not denied, and will eventually be sent.

RecipientRateLimit

It limits the number of recipients that a user can send to in a 24-hour period. The user will receive an NDR for messages if he exceeds this limit.

To create a new policy where the users can send to 100 recipients a day and no more than 2 message per minute, you would use this command:

New-ThrottlingPolicy -Name NewthrottlingPolicy -RecipientRateLimit 100 -MessageRateLimit 2

To assign this newly created policy to a user use the following cmdlet

Set-Mailbox -Identity user_alias -ThrottlingPolicy NewthrottlingPolicy

Another interesting fact here is that  Throttling policies get applied to mailbox, so If you are using From address then From address email address mailbox throttling policies will not be applied rather your own mailbox policy will be applied.

More Information

Read more about Message Throttling with Exchange 2013 Here

Understanding Client Throttling Policies with Exchange 2010 Here

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An automobile enthusiast at heart and computer geek by profession, started my Career with MS in 2005.Left Jobs and started Pledge Technologies (the parent company to Grishbi) back in 2009.We have been providing IT consulting to various Small and Medium businesses across US and UK since then.Our company specialises in Microsoft Server technologies like AD, Exchange, the rest and with numerous Office 365 migrations under our belt, we quite an expert with that too. Whatever we learn in our day to day life, we share it back on Grishbi as a Thank for all the love and support our customers have given us.
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