My reason for thinking, in my original post, that the wrong host address is being used is that the ConnectionError above contains 0.0.0.0 in its url for /3.1/domains/... but 0.0.0.0 is only present as the listen address on the core web service and does not appear in the config for postorius.The ConnectionError above comes from requests.request (docs at <https://requests.readthedocs.io/en/master/>). Client only provides a URL in the call to request and the URL is the baseurl + the path and the baseurl is MAILMAN_REST_API_URL which you have as http://greyarea-post:8870. Entries above have http://greyarea-post.cam.ivimey.org:8870/. Is that the correct FQDN?
I suspect a DNS lookup issue. How does greyarea-web1 resolve greyarea-post? You could try a FQDN that greyarea-web1 can lookup in DNS rather than relying on /etc/resolv.conf and/or /etc/hosts.
No, ignore that... I edited the FQDN down to the hostname in the email for simplicity, but even if it was in the log the hostname does map properly (i.e. host greyarea-post and host greyarea.cam.ivimey.org return the same thing).
In referring to the ConnectionError from:
'ConnectionError(MaxRetryError("HTTPConnectionPool(host=\'0.0.0.0\', port=8870): Max retries exceeded with url: /3.1/domains/ch-bc.org.uk (Caused by NewConnectionError(\'<urllib3.connection.HTTPConnection object at 0x7f5416db8518>: Failed to establish a new connection: [Errno 111] Connection refused\',))",),)')
if you reconstruct the url passed in it was presumably:
"http://0.0.0.0:8870/3.1/domains/ch-bc.org.uk"
... and if that is correct I am not surprised to see an error message.
But perhaps that isn't what it was...
Ruth