Hi, I was able to rebuild mail receiver docker using instructions at that link Direct-delivery incoming email for self-hosted sites - howto / sysadmin - Discourse Meta
Had to upgrade / resize my Digital Ocean droplet to do it, as even after deleting all backups etc stored on host, there was not enough disk space to do a rebuild
After rebuild, I was able to send that message to staff@nzarchitecture.net.nz - and the forum log this time acknowledged it.
However when I try to reply by email to an existing topic of the forum that I have been notified about, while the incoming messages are now acknowledged, none appear on the forum, and all get Mail Delivery Failure warnings in email log.
Incoming messages are not appearing in Bounced Email log, but do all appear in Rejected Email log with warning [Email::Receiver::BadDestinationAddress] - including my own administrator email account which I would hope does not suddenly have a bad destination address