So I'm setting up a personal mail server, which is running on my home network using postfix and dovecot. At the moment, my domain name points to my home network's IP address, and I have port forwarding set up for port SMTP, SUBMISSION and IMAPs.
I'd like to set up an external server to act as a proxy in all of this. So when receiving mail, it goes to a postfix instance that then connects to the postfix instance on my network and asks if the delivery address is valid, and if so, then LMTPs the message into my server to handle the rest of the delivery (spam filtering, choosing a mailbox etc).
When sending mail, if I'm on my home network, then my mail client should submit it to the home network's postfix server, which does all the authentication checks, and then should then pass it to the external postfix server, which then sends it to it's mail destination on the internet. When I'm outside the home network, I'd want the client to submit it to the external server, which checks asks the home server to confirm the authentication details it has been provided, and then send to it's final destination.
Where I'm having trouble is getting the two postfix servers to talk to each other. I got external dovecot talking to home dovecot fine, but I'm completely lost in getting postfix to co-operate.
Anyone have any advice on how I would proceed from here?