How to force Postfix to send to MX server and not locally?

Question

Domain Name System

The situation is as follows, the smtp server is located separately from the pop server where incoming messages come (priority MX). All incoming and outgoing external letters go horsho. The problem is that when sending a letter to the e-mail of the same domain, or to the sender's e-mail itself, the letters arrive at the server that is used as smtp, and not at the main MX.
When pinging the MX server from the smtp server, the correct IP is displayed, that is, the IP of the MX server, therefore sending the letter does not go through the dns server to find out the address of the MX server, I just return to the same local server.
How to force local letters to go to the main MX?
Thank you.

Answer 1

https://debian.pro/1139
In the article itself - a description of the answer to the question "what the hell?", and in the comments - a link to how to do the same in postfix.

Answer 2

How much such slag I shoveled until I got into the documentation)
www.postfix.org/STANDARD_CONFIGURATION_README.html...