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.

  • What are the results of trying a manual smtp connection from your internal SMTP server to the external server you are trying to relay through? (telnet <server name/IP> 25). This should let you see if the SMTP connection is succeeding. Looking through your SMTP logs for the failure message (or the mail queue for deferral reasons) could also be helpful. – BeepBeep Mar 9 '15 at 15:36
  • @beepbeep it works. Any email sent in LAN pointing to this smtp gets relayed to Google smtp server... But it stops there I need my colleagues in other country to be able to use this smtp to relay it out from other countries as well.. – Guang Ming Chng Mar 9 '15 at 15:38
  • I've not used google for relaying, perhaps it is dropping your email if seen as an attempt to use it as an open relay. Is this a google service you are utilizing (that is expecting to allow emails from your domain to be relayed through it) or are you just trying to point it to a google smtp server and relaying through? – BeepBeep Mar 9 '15 at 16:47
  • @beepbeep it is a open service? Anyone could set up a local smtp to relay outbound email to Google smtp. The authentication is still with your credential. – Guang Ming Chng Mar 10 '15 at 1:11

I edit my firewall and allow port 25 and smtp started working right after I do a restart for the smtp relay server.

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