How to correctly configure mail redirection from a server on the local network to the outside through a proxy machine?

Question

linux

Good afternoon. Prompt the direction of research. The situation is as follows:
There is a local area network isolated from the Internet. It runs redmine, which can send mail about task changes, but since the server is isolated, no one set up mail. In the same network, there is one machine that has access to the Internet.

How to make it so that the mail from the machine with redmine goes to the machine with Internet access, and from there it is already sent to the recipients?

Answer 1

In short, install postfix/exim in relay mode on a "machine with Internet access".