I have got a local smtp server to relay to Google smtp so as to increase the limit of email recipient from 2,000 a day to 10,000 a day for specific users.
I can send through this local smtp relaying server of mine in my own Lan. But if I were to try to send via this smtp using a public IP that is NAT to the internal IP address, nth goes through.
Other than allowing firewall connection port, any other idea why is this happening?
Note: ICMP request through the public IP, done externally is successful.