Setting up DNS on Winsows 2012 to work with a mail server

Question

Domain Name System

And so the situation is as follows:
The authorities set the task to raise their own mail server. I've never encountered this before, so (of course) there were difficulties. I deployed Hyper-V server 2012 R2 on the server, raised a virtual machine with kubuntu on it (I previously worked with it) and deployed iRedMail on it. The network structure is as follows:
1. Internet comes to the Mikrotik RB2011 router
2. DHCP, DNS, AD, WSUS, file server - to Windows server 2012.
Mail works only for sending, but it is impossible to answer these letters. Which, in general, is logical, since no one will be able to find this domain name assigned to the mail server. Forwarded ports on the router 25, 443, 22, 80 dst-nat to the local mail server - now when accessing from the outside, we immediately get into the mail interface for users (but only when writing an external IP). From the internal network, only the internal address of the mail server can get to the mail user interface. On the mail server itself, the transition occurs if you write a domain name (which is quite logical, since it is registered in hosts). I think the difficulty is only in setting up DNS, but somehow I just can’t figure out how to debug it so that letters come to this mail. Added the domain name of the mail server and the local ip address to the forward lookup zone.
Can anyone advise on this? What ports still need to be registered, where to redirect ... There are a lot of questions, and there is not much time for trials, so I ask such a childish question here.

Answer 1

"I added the domain name of the mail server and the local ip address to the forward lookup zone." It seems to me that your server serves only the internal DNS.
1. Do you have a domain name mycompany.ru (do you have a website?)
2. Who did you register it with?
3. Call the company that registered the domain name (they probably have the password for the DNS control panel) and ask them to add an MX record to mail.mycompany.ru and an A record mail.mycompany.ru=ip of your server.

Answer 2

the first thing is to set up mx records in dns in domain management and examples of settings
www.prodmag.ru/mdaemon/instructions.php
www.freebsd.org.ru/handbook/mail-advanced.html