Thanks!
So - I've documented what I did below. Now that I am getting bouces, I got an email that said "The response from the remote server was: 550 5.1.1 <test@emaildomainA.com>: Recipient address rejected: User unknown in virtual alias table"
Specifically to some ot the questions above:
What do you mean by "set"? That the list has archiving enabled?
Yes. I meant that archiving had been enabled for the test@emaildomainA.com test list.
Shunting error: I think the shunting error is a distraction if it is caused by not having a recipient. Early tests to the test list had me as an administrator, but not as a member - so this would have caused that. Once I added myself (before I sent the original message in this thread), the result (not sending the message to the list using a 'virtual' domain and not archiving it) continued.
Virtual Domains: So based on the Postfix virtual domain documentation and the Mailman3 specific "Unusual Postfix configuration' section, I added the following to my postfix main.cf file: virtual_alias_domains = emaillistA.com emaillistB.com virtual_alias_maps = hash:/opt/mailman/mm/var/data/postfix_vmap and removed those domains from the 'mydestination' setting.
I then created the postfix_vmap file and added to it: emaillistA.com DOMAIN # emaillistB.com DOMAIN
...then ran postmap with the path and reloaded postfix.
On testing I also noticed that a previous counce was to emaildomainC.com - an alias for emaildomainA.com I had originally setup in the Postorius domain setup and then removed. I guessed that it was still in the postfix config, so I double checked in the MM generated postfix_domains file and ran postmap /path-to/postfix_domains and reloaded postfix again...and sent another test message....
This then generated the error email at the top from my email client (gmail).
...but the end result is no email sent and thus the reason there is no archive....
Any further suggestions? I can supply other log messages and configuration options if it helps.
Duane