Usually – No, you cannot.
The idea of the private team network is that the participants are in a private area of authorized users only. Each account can communicate only with users from its network. If you want to have contacts from another network you need to create an account in that network.
But, Brosix created a feature called Network Connections. This allows Team administrators of two Team Networks connect their teams. Then under their full control they can allow specific users from one team to communicate with a specific user into the other team.
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