Hey sorry for the dumb question. But, trying to understand if PMG same as using a email server like iRedMail? Is the gateway providing same as a typical email server? Are folks using PMG + a Email Server? Can PMG act as both?
The PMG doesn't have a webmail like webinterface for end users, it offers a good webinterface for (mail) admins though.
So normally you'd put that service on another server. You could naturally always use Proxmox VE to have both on the same physical server as Virtual Machines or Container appliance. This gives you a good separation but still low overhead.