OU list is empty when adding new user or group

I ran into this same issue and got tired of manually re-applying the web.config fix after every cumulative update, so I automated it.

The problem is that Exchange CUs overwrite the web.config file and remove the GetListDefaultResultSize key every time. I created a PowerShell script with a scheduled task that:

Checks the ECP web.config for the GetListDefaultResultSize key

Adds it automatically if missing or updates the value if too low

Creates timestamped backups before making changes

Restarts the MSExchangeECPAppPool to apply the fix

Runs daily so you never have to manually fix this post-CU again

GitHub repository: https://github.com/digitron64/ECPFix

Works on Exchange Server 2013, 2016, 2019, and Subscription Edition (SE). Must be deployed to all Exchange servers with the Mailbox role since ECP requests can hit any server in the environment.

The repo includes the PowerShell script and pre-configured scheduled task XML. Tested and working across our three-server environment.

Hope this helps!

@Evgeniy Goldshtein

Yes, you need to change it for all Exchange servers. I noticed you said "I added it again on all servers", so I didn't mention this one in the first step of troubleshooting.

When you login EAC from Exchange server A, this request may be redirected to another Exchange server (as far as I know, it effected by the DNS record and where your admin account hosted) , so you need to change this one on all Exchange servers.

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@KyleXu-MSFT As I said, we do have more then 500 OUs and used this web.config trick for years, it just stopped working.

Anyway, I found the problem: After the last update when I copy/pasted the line into web.config on all servers, I didn't copy it right on 1 of them (out of 10). I'm not sure why all the servers were affected, but after correcting it it started to work!

Thanks everyone!

@Evgeniy Goldshtein

It happens after every Exchange update, so as usually I added it again on all servers. But his time it did not help!

From this article, we can know that this is expected behavior you need to add this value every time that you install a cumulative update.

I suggest you use the command below to check the number of OU in your organization. Then use a use a close value in the configure file. Such as using 510, if there exist 500 OU in your AD.

(Get-OrganizationalUnit -ResultSize unlimited).count  

If it doesn't work for your Exchange server, I would suggest you update it to the latest version Exchange Server 2016 CU23 + May22SU: This value could work in this CU (I set this value to 1)

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