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.
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