Exchange Online EWSMaxSubscriptions throttling budget calculation has been updated!

We have made a change to the way that Exchange Online accounts for the number of subscriptions against the EWSMaxSubscriptions throttling limit.

In earlier versions of Exchange Online, the throttling limit was calculated against the calling account. A calling account, which can be one or many client applications or a service account targeting many mailboxes, was limited to 20 notification subscriptions. This subscription limit restricted Exchange Impersonation scenarios in which a service account accesses a large number of mailboxes. It limited a service account to at most access to 20 different mailboxes, assuming one subscription per mailbox, or 20 subscriptions on one mailbox. This was not very scalable. For example, if a service account had to access 5000 mailboxes, you had to have 250 service accounts to account for this limitation.

Starting with service mailbox versions 14.16.0135 and 14.15.0057.000, this limit has changed. Now, the charges are counted against the target mailbox rather than the calling account. This way, a service account can create subscriptions against many more than 20 mailboxes. One benefit of this change is that you can now design a service application that targets Exchange Online and Exchange on-premises using a similar code base for subscription management. A single service account can now service up to 5000 subscriptions.

Customers, you asked for this change, and now you have it. Subscribe on!  

Comments (8)
  1. mjb says:

    now if only we could change throttling policies overall. Archiving and Migration apps are pretty much useless in Exchange Online due to the EWS throttling

  2. jay c says:

    mjb, I'm pretty sure you can change any throttling policies you want. You can even create a new policy with all custom values and assign it to a single mailbox.

  3. jay c says:

    Maybe not for online accounts (i have no experience there), but for on-premises Exchange organizations you can.

  4. IMPORTANT: The Get-ThrottlingPolicy and Get-ThrottlingPolicyAssociation cmdlets are not available with Exchange Online. In a previous post, Exchange Online Throttling and Limits FAQ, I stated that those cmdlets were available. That information was true when it was posted. These cmdlets are currently only available with Exchange Server.

    1. Abd-ur-Rahman says:

      Has there been any recent update in above context or the above limits hold ?
      Will this 5000 subscriptions also work for delegation ? i.e If I give delegate access of than 20 mailboxes to a single account and then do push subscriptions for them. Will this be the same Or do different limits apply to delegation?

      1. Hello Abd-ur-Rahman,

        I’m sorry that I can’t answer your questions. I haven’t worked in this area for quite some time so I have no insights into the current state of throttling for Exchange.

        With regards,

  5. Sergiu Indrie says:

    Hi Michael,

    I have 2 questions:
    1. Is this 5000 subscriptions limit documented anywhere?
    2. In order to reach that 5000 subscription limit do we need to use 200 subscriptions with 25 subscription connections? Or can we have 5000 subscription connections with a single subscription each? (I’m guessing we might exceed the EwsMaxConcurrency limit which is set to 27 as far as I know)

    1. Hello Sergiu,

      I’m sorry that I can’t answer your questions. I haven’t worked in this area for quite some time now.

      With regards,

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