Which server to choose and how to set up for mail on the local network without access to the Internet?

Question

Mail server

Good day!
The bottom line is this, I need to deploy an e-mail server that would work exclusively for receiving and transmitting mail within the corporate network (without access to the Internet)! I want to upgrade to Linux. I decided to ask you, so as not to make mistakes in the sweep and setup!

Answer 1

raise internal dns + iredmail and enough