The server is already set up this way. Let me clarify what I mean.
I want to accept incoming mail destined for users in the local domains (mydomain.net, mydomain.com, mydomain.org) only from the McAfee SMTP servers and no where else. The McAfee servers don't provide any authentication and have to be filtered or recognized by their IP address range. The MX records for my domains point to the McAfee servers, but anyone could attempt to send mail or relay thru my server here by using its IP address directly, instead, so,
I do not want to accept mail from any other servers either destined for the local domains or in any relay attempts thru my server, except if authenticated as a user, that is, I want to relay mail from any authenticated user (myself and the other authorized users) both from within the LAN (on 192.168.0.0/20) or from the outside.
The mail server I currently use has a mechanism that will recognize servers from a specific IP address range as a limited-privilege user ('guest' or whatever I designate) that is allowed to drop mail that's destined for the local domains, only.
Is there a way to do this in Postfix, or does it already do so? Would you please explain a little about how Postfix might accomplish this?