In postorius(a)host.name.com, please change the host.name.com to match the MM3_DOMAINS or whatever it is called in your MACROS. Remember, it has to be a VALID hostname that you will be using for Mailman3 lists. That, coupled with the IPs 172.19.199.x being in relay_from_hosts should let the address to pass verification with Exim.
The problem turned out to be not using a valid email account to send out admin related emails coupled with:
verify = sender
I did have a valid domain setup in the macros file and I had the mailman only IPs listed in the relay_from _hosts setting however that was not enough to get past the verification error. Once I commented out verify = sender, then the error message went away. I will be getting a valid mailbox setup today for posterius@host.name.com today so I can turn the above setting back on.
Brian