How to get Postfix to send/forward/relay to a sub-domain located on another server?

Question

I have a quick question. How do I setup postfix to send an email to another server (Exchange Server) when sending to an email address that has a sub-domain of our main server. For example, say our main server is mail.example.com and we have a Exchange server setup to receive emails from exchange.example.com. We have the MX records setup in our DNS and it receives correctly if we send from a GMail account. However, when we try to send an email from a @example.com account we get the following error:

Host or domain name not found. Name service error for name=exchange.example.com type=A: Host not found

I believe Postfix checks for local mailboxes first and if its setup with the domain it delivers to the local account, but in this case the sub-domain accounts are located in another server. Anyone have any thoughts on what I need to do within Postfix so it doesn't look locally for the exchange.example.com mailboxes?

Thanks for your help.

Answer 1

It sounds more like the machine cannot resolve host names... So use your favorite editor to supply name servers to the system.

sudo vim /etc/resolv.conf

The contents of that file...

nameserver 8.8.8.8
nameserver 4.4.4.4
domain example.com
search example.com

And maybe edit /etc/hosts and add the hostname and IP address:

sudo vim /etc/hosts

And the line to add (use the real IP address)...

192.168.1.100 exchange.example.com exchange