I run a few virtual servers at home behind a NAT, including an e-mail server, with dynamically updated dns records pointing to each of the servers. Consequently, I suffer from the loopback problem when working with these servers from my desktop PC. (E.g., I ping one of the dns hostnames and the ping goes to my router instead of the server). I fixed this problem by manually adding the in-home IP addresses and name pairs to my /etc/hosts, and then setting /etc/host.conf to a "hosts, bind" order.

This seems to work for every application on my desktop except for one: the postfix installation on my desktop PC (used for mailing smartctl messages and so forth) cannot communicate with my in-home e-mail server (times out). I checked the logs, and it looks like it is trying to use the IP address from the actual A-RECORD, rather than the address in my hosts file.

So I'm not quite sure what to do. There seems to be a "proxy_interfaces" parameter in main.conf which might be relevant, but I think it only deals with received mail. I'd prefer to have the mail going to that e-mail server, rather than also having to check the spool on my local desktop accounts.

more likely, the "problem" is that postfix is using the MX record. it falls back to the A record when MX isn't available.
you can override MX lookups with a transport table or its variants. but, a better solution might be to have the router do a destination address rewrite (when an in-LAN machine accesses another in-LAN machine using its external IP), or even to run an in-LAN DNS server having the private addresses.

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