Why is mail not passing between my Exchange servers?

The NG Firewall Server forces Extended SMTP (ESMTP) to fall back to SMTP so that the transmitting emails may be scanned. When two Exchange servers are setup such that they require ESMTP communication, all communications will fail. This is enforced by transparent rewriting of the "EHLO" command to "HELO" and appropriate keywords are also stripped.

This can be fixed by adding a Bypass Rule for communication between the servers.