Exchange 2016 – AirSync Exceeded Errors

As an Exchange admin, you have come across a number of errors in the event log you cannot just fix or explain and one of them is the common error below (I have had a lot of questions regarding this so thought of posting it here):

  • Exchange 2016 Event ID 9646 AirSync exceeded the maximum of 250 objects of type

If you look on the internet, which I am sure you have done, there are articles saying just change a registry key and it will go away. The problem is you are not addressing the root cause, you just masking it. The registry change I am referring to is as per the following showing the registry path and key below:

  • HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\MSExchangeIS\ParametersSystem\MaxObjsPerMapiSession

The key is called: “objMessage” and it has a value of 250 which is the default. If you go and change the value to 1000 for example and reboot that Exchange server, you may have no errors logged in the event log until the device triggering it hits the value of 1000 and then it will start again.

The way to resolve this error permanently is to find the end users mobile device that is causing it. If you are in an organisation that has thousands of end users, this may become a challenging task but do not look at it that way. You may find that you have end users running devices that have older iOS versions or Android versions and this triggers these alerts on the Exchange server. If you open the IIS logs, yes there will be many, however you will be able to identify the device used or simply look at the error message in the event log to get the user details at the end of the message.

This alert triggers because of the ActiveSync version used by the client. I spent endless hours testing this in a lab with different versions of Exchange, from Exchange 2013 right up to Exchange 2019 and each one of a different CU, moving up to the latest one. My trusty Samsung Galaxy Note 4 I used for testing kept popping up each and every time, yes this is a device that is old and does not get anymore Android updates and I was testing with the application called Microsoft Outlook (still wonder how it worked on this version). When I borrowed an iPhone running the latest iOS, I did not receive an error message in the logs but I did constantly for the Samsung device.

I also tested this on a RedMI device that has it’s own flavour of Android OS and also started seeing the errors coming through in the event logs. I also tested using the Native Mail application on all 3x devices and only the older ones reported an error in the event logs. Basically the ActiveSync version on all 3x devices were different and from what I could see this was not an Exchange 2013, Exchange 2016 or Exchange 2019 issue but rather a software issue.

Some people messaged me to ask if this was maybe a DAG (Database Availability Group) issue and I tested in my lab with the same results, latest iOS using native or Outlook app gave no errors but the older devices did. Another question came up if this was a load balancer problem. I got hold of the free load balancer at Kemp (thank you guys for this) and set it up (wrote an article on this if you want to take a look) and again the results were the same. No vendor should be blamed for anything here, it is merely an OS issue on the older devices.

This does become tricky because you cannot tell thousands of people to go and upgrade their devices. As a work around, you could ask them to restart their devices maybe once a week so it does not keep consuming sessions and flushes until such time they do upgrade because applications like WhatsApp etc. only work on newer models. The error is a tricky one to handle but increasing values in the Registry is not the answer as those devices as mentioned will eventually use up those resources and you are back to square one.

Maybe you have old devices at home as you upgrade frequently and you could possibly help someone out who cannot afford to upgrade.

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