I'm running Postfix 2.10.1 on the same server as my webserver so the domain is example.com and it is receiving mail locally but not from any external networks. The server is running CentOS 7.
For the DNS, I'm not exactly sure the proper settings. I currently have an MX record for example.com and a default A record with the IP of the server. All of the resources I found online were using a subdomain like mail.example.com and then had a corresponding A record. I've tried it both ways, where the A record points to the same IP address, but it didn't seem to make a difference.
For the Postfix configuration, master.cf wasn't changed and I made the following changes to main.cf:
myhostname = example.com mydomain = example.com myorigin = $mydomain inet_interfaces = all inet_protocols = all mydestination = $myhostname, localhost.$mydomain, localhost, $mydomain mynetworks = 127.0.0.0/8
The following TCP ports are also open: 25, 465, and 587.
Additionally, I was also curious about mail_owner. None of the resources I read mentioned it or creating a user for Postfix. Should I create one, and if so, what files/directories should it own, if any?