The central issue is how to get SME to send a copy of every mail, both incoming and outgoing, to that local archive box.
Every attempt ended with all mail getting sent to his smarthost, including the copy mails destined for the local archiver box.
But the command
db domains setprop archive.dc.local MailServer 212.*.*.*
tells the SME server mail system to forward all mail processing for the domain
archive.dc.local
to the server at 212.*.*.*
This should be all that is necessary.
It's not a hard thing to do, I have done it before & it works fine.
I believe Gordon Rowell added this functionality many years ago.
AFAICT Drifting probably has some resolution issues on his network, the pilar server is not being seen by the SME server (my guess).
SME server usually acts as the gateway, so all mail is processed by SME server in a typical LAN.
If you want certain mail for a certain domain to be processed by another server, the steps I outlined are the way to do it, including how the other domain is configured on the SME server.
It would be good if Drifting answered the various questions posed as the answers are pertinent.