I'm assuming this is going to be a no but I'm looking for a way to control who particular users can or cannot send email too. I know I can control distribution lists and the visibility within a PO for users/DL's. What I'm looking to control is to make some users unreachable via email from other users.

Example: User A is only allowed to send emails to users B and C and no one else. All users other than user A can send to users A through Z. hope this helps.

GW 2014 SP1(Linux)