Have all bulk email sent as BCC, so that replies only go to the sender not to all on the original email. Ideally the sender should decide how to send, but if no choice then for privacy reasons all should be sent BCC NOT via a TO field, which provides access ot others' email addresses.
I believe this is already implemented. Whenever I go to Send a communication and click the "Open list in e-mail client", it always puts the addresses in the BCC field.