DNS settings for building a postfix email server

DNS settings for setting up the postfix Mail Server-Linux Enterprise Application-Linux server application information. For details, refer to the following section. Hello everyone, I'm glad that you have browsed my post. The problem is that the postfix email server has been set up, but you can only send emails and cannot receive emails. After careful query, I found a problem with the DNS settings on the server side. But I don't know how to set this. For example, I have an email domain name, abc.com. The Internet address is 220.221.233.121, and the Intranet ip address of the local machine is 172.16.5.5, in the domain name management system, the domain name has been directed to the Internet address (220.221.233.121), and my local dns is not set. How can I set it? Can it be specific? Thank you very much!