The solution to the problem is to add your users to a group that does not have an Organizational Unit designation.
In your Groups folder, create a new Group that you can assign all existing members to. Make sure that you do not designate the group as an Organizational Unit
To find all existing users of the group, you can use the Admin > List Directory menu command.
Click in the list area and choose Save As.. and save the file that you will now open in Excel or some other spreadsheet that we will use to build the new script.
You can now open this text file in Excel or some other spreadsheet and start at Line 13 to bypass the headers
Remove all Columns except for the UserID column and place it in Column 2
Add the text "PGADD" to column 1, and the name of your new group to Column 3 and fill down the list
Send a new command to Populate the Staff Mailing List with the new group name
REPLY
POPULATE GLOBALMAILLIST "Staff Mailing List" 1 StaffML
Verify that the mailing list has been cleared and populated now only with users.
NOTE: You must make sure that when you create new users who are members of your key group or add users to this group, you must also add them to the Mailing list group.