Traffic Source: {65.75.85.95}
Traffic Service: SMTP
Traffic Destination: External (Address) {or whatever is the target of your MX record}
NAT mode: DNAT (Destination)
Destination: {10.20.30.351} {it may work if this is left blank - I'd be interested to know if someone tries it blank}
Destination Service: {leave empty when not changing}
Automatic
packet filter rule: {unchecked!}
Traffic Source: {65.75.85.95}
Traffic Service: SMTP
Traffic Destination: External (Address) {or whatever is the target of your MX record}
NAT mode: DNAT (Destination)
Destination: {10.20.30.351} {it may work if this is left blank - I'd be interested to know if someone tries it blank}
Destination Service: {leave empty when not changing}
Automatic
packet filter rule: {unchecked!}