We are new to this client and the previous provider set up three exchange servers for different purposes. 2 for delivery of bulk mail (they send subscribed advertising) and one more for the internal users. Each is a mailbox server and a hub transport server. They are each NAT'd to their own external IP in order to protect the users' server from the blocks that happen on the bulk servers.
The problem is that the outbound delivery does not work like that and all hub servers are automatically distributed and users email is being sent by the bulk servers (and then getting blocked).
What is the best way to fix this without adding additional servers as edge servers? Is there a way?