> As you can see above, with "inet_interfaces = all" Postfix will > LISTEN on all available IPv4 (or IPv6) interface addresses, and it > will NOT BIND to a specific IPv4 (or IPv6) address.
Sorry if I'm being slow. Yes postfix will listen to ALL and bind to 0.0.0.0:25 What is unclear to me is what will postfix try to use when making an outbound connection when the server has two interfaces, first interface only has one public IP, and the 2nd interface has only one private (192.168.x.x) IP. Will postfix randomly try the private IP to deliver outbound mail and fail? And if it does fail, does it instantly try again or go back into queue to try again later until it randomly uses the public IP?