Scenario: Exchange 2007 (no Edge, one server with mailbox role, one server with hub+cas roles) behind a FortiGate appliance Problem: As soon as the UTM part of the FortiGate appliance is enabled, I had a lot of 451 4.4.0 and 400 4.4.7 errors shown in the message queue (outgoing) Solution: First, I had to check … Continue reading Exchange 2007, FortiGate UTM,Error 451 4.4.0 and Error 400 4.4.7