This solution if we want use 2 smtp smarthost (failover) as sender email.
– Install Postfix Forwarder
– Open Postfix Forwarder (Services –> Postfix Forwarder)
type on custom main.cf options
relayhost = [smtp.smarthost1]
fallback_relay = [smtp.smarthost2]
When connection smtp.smarthost1 Down, email send from smtp.smarthost2. If connection UP, email send from smtp.smarthost1 again.
– Give permission server can relay to PFSense (send email through PFSense)
CMIIW, Thanks 