Here is the general information about emailing members:
To protect your privacy, only your friends and certain members of social networks you belong to can send you messages on Ning. If you’re a member of a network, the Network Creator and Administrators can send you messages and you can message them back. Further, if you belong to any groups, the Group Creator and Admins can get in touch with you privately — and you may receive messages sent to all members of a group. In order to send another member of a network a message, you’ll need to ask them to be your friend first.
So, as long as you email a member who is your friend, then that's okay. I don't think you can email your friends as a group, though.
If so, someone else chime in with instructions. Thanks!