Tilmann,
The level of groups I was thinking of, is clubs or classes as in a .lrn environment. I don't know how this could be implemented, I'm not familiar with openacs4 API and data-model. At Uned, we have a acs3 site in which we configured this privacy level so students may share their personal data (email, address, phone, etc.) only with their classmates. Also, the privacy level chosen for email can be different then the one chosen for address or phone.
