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

It depends a bit on your needs. My proxmox setup is like multiple nodes (computers) with local (2 drives with ZFS mirrorig), they all use a truenas server as NFS host for data storage. For some things I use conaitners (LXC) but other thing I use VMs.

It is, I looked at several vendor’s and it’s all te same except for the nice gui. They all have their own blacklist that they feed with the spam/ham queries from their devices.

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.