Hi,
Welcome to the Microsoft forum!
I tested the restriction ,and set that only “jake z” can send message to the distribution group, and then I send a message from “mikehu”,it didn’t alert "You don't have permission to send email to Distribution List” at first:
But after a while,I tried again,and finally it shows the alert like:
So I recommend you to use OWA to avoid outlook client or other reasons.
You can try to run the Command : Get-DistributionGroup -Identity testDL | Format-List (Replace “testDL” with the actual identity of your distribution group)
Check the following three attributes:
AcceptMessagesOnlyFromWithDisplayNames
AcceptMessagesOnlyFromSendersOrMembersWithDisplayNames
AcceptMessagesOnlyFromDLMembersWithDisplayNames
If the members of the list appear correctly in the results, the restriction has been successfully applied, but this may take some time to take effect, so please wait for a while.
Hope this helps.Please feel free to contact me if you need more support.