Secara logika seperti ini :
1. Di firewall filter forward ->
a. in-interface=WAN dst-address=<ip local mail server> dst port=25 accept
b. src-address=<ip local mailserver> src port=25 dst port=1024-65535 accept
c. src-address=<ip local mailserver> src port=1024-65535 dst port=25 accept
2. firewall nat
a. src nat, src address=<ip local mailserver> to address=<ip publikmu> port=0-65535
b. dst nat dst-port=25 to address=<ip local mailserver> port=25 in-interface=WAN
Rule ini so far berjalan dengan baik di clientku.
semoga bisa membantu.
