I'm not sure of what you are asking. Groups are not set up with Os or OUs, they are simply group documents. If you have a group called engineering, its Internet address is email@example.com. People inside that group will receive the message. There is a field in the configuration document under MIME Settings –> Advanced –> Inbound called "Remove group names from headers." If that field is set to "Yes," then all messages from the Internet to group names will be trashed and not delivered to the groups.
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This was first published in October 2004