When I added permissions to add/remove members to a user in Child3 domain for the Universal Group (in Child1 domain). "Write Members" special permission supposed to give the user to add/remove members from the DL using Outlook.
But, it didn’t for the user in Child3 domain. Owner for the DL who resides in Child1 domain is fine. I found the following KB article which is my issue.
I didn’t bother using AutoDL. But that would be a right solution. Instead, I informed the user in Child3 domain that he can’t add or remove member because of different domain.
If there is only one owner for this DL, I would move the DL to the Child3 domain. If you have same issue, you may consider these options.