Np good luck with the project

After you setup the mail gateway you can telnet to port 25 and do the command line mail test and see if mail is delivered to your mail server. After that is confirmed you change your dns mx records.

There is not much to document on how to set it up. The gui is very intuitive.

You need to setup the relay domains, transports and Options>DNSBL under configuration > mail proxy

They don’t have to cost money. The mail filter appliances are all based on postfix, spamassassin and a virus scanner like clamav. The thing you pay for is the nice gui.

I recently moved to Mailcow, it’s a one in all solution. My spam filter is Proxmox mail gateway, also very user friendly.

I also have a mail filter, I have been hosting my own mail server for the last 25 years.

Yes, that works just fine. Wen my daughter was at her boyfriend’s place she used a wireguard tunnel to my house to use Netflix.