Exchange 2019 cannot display all user when add allowed sender in delievery management

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!

Hi @Anonymous ,

<!-- allows the OU picker when placing a new mailbox in its designated organizational unit to retrieve all OUs - default value is 500 -->
<add key="GetListDefaultResultSize" value="2000" />

According to the official documentation, the command is used to solve the complete list of organizational units (OUs) isn't displayed as expected. This does not apply to other situations.

To my knowledge , there is no official document that explains the number of mailboxes to be displayed in Delivery Management, and guidance on how to change the maximum number of mailboxes displayed .

If it is possible , I suggest you could refer to the following cmdlets to export them to csv for filtering.

Get-Mailbox -ResultSize unlimited | select-object DisplayName, userPrincipalName | Export-CSV-Path c:\share\mailbox.csv  

Then refer to the following cmdlets to add allowed senders:

Set-DistributionGroup -Identity "******@contoso.com" –AcceptMessagesOnlyFromSendersOrMembers @{Add=“******@contoso.com”, “******@contoso.com”;}  

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Use Exchange Powershell instead

(Get-distributiongroup <group>).AcceptMessagesOnlyFromSendersOrMembers