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I am having problems getting my mail server to work. It used to work fine when I was connected directly to the Internet but I had to move the machine and it is now behind a NAT router. I have setup port 25 for SMTP through the NAT but when I try to send a message it says that it can't connect to the remote host. The remote server IP gets resolved ok but it doesn't seem to be able to connect to it.

My FTP and Tomcat servers are working fine, so I suspect the problem has something to do with the fact that my router not only does NAT but also gets its external IP from a pool, so I don't know how to configure JAMES to get the dynamic external IP.

After testing through MailTester.com, I get that the connection times out, and since I'm quite sure I have the smtp and pop3 ports (25 and 110) properly open on my router, it seems that JAMES doesn't bind to my external IP, and I have no idea how to fix that.

Any help would be appreciated.

NWOD
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(...) but also gets its external IP from a pool, so I don't know how to configure JAMES to get the dynamic external IP.

I don't know how James is operating under the hood, but I guess it must bind to some ip address and wait for connections to come in. Problem is, if it has a private ip address and if the NAT does not know it has to redirect port specific traffic to your James server, things are not going to get connected by themselves.

If your server can be assigned a public IP address, then do so. It is the simplest. If not, then assign it a fix private address and configure the NAT to forward all port-relevant traffic to it.

On the other side, it is (nearly) impossible to predict how the NAT will translate private IP address into public addresses for the WAN. Any solution to your issue should NOT rely on this translation.

Jérôme Verstrynge
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  • I have seen reference in other questions on James that mailservers require static IP addresses and will refuse mail from DHCP servers. – Thufir Aug 17 '12 at 05:26