Adding users to "Accept messages from" field in Exchange Tab

Adding users to "Accept messages from" field in Exchange Tab

Hi. I am new to AD Manager so just starting to learn its usefulness. I am trying to modify a Distribution Group by adding USERS to the Accept Messages from field but I two issues. 1) I can only add one at a time which is quite slow. Any options for bulk adding? 2) When I search for a User I get no results. I think it's only listing groups.
Thanks
Alex

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