Problem

Messages from a IP/Host/Domain gets rejected by MailGate.

"421 Service Not available" error is returned by MailGate when one of the Edge defenses comes into play for the connecting IP/Host/Domain.

Connection Tracking for that IP/Host/Domain should provide the reason for blocking (blacklisted/ DHA, DoS etc.) and allow to unblock.

This situation can be avoided by adding the IP/Host/Domain in the External hosts domains under Relay Policies -> External Hosts/Domains with "Accept" connection policy so that no defense checks are performed on it.