@loudlemur Here are some of the possible trouble indicators in the logs (I have obfusticated the domain names/email addresses)
One clue might be that though I am actually able to send mail, none of it appears in the "Sent" folder.
Also, if I go into "Manage folders", i can't create a folder or even click on those toggle buttons on the "inbox" for example. They don't respond.
Dec 17 17:09:50 (node:90) [DEP0123] DeprecationWarning: Setting the TLS ServerName to an IP address is not permitted by RFC 6066. This will be ignored in a future version.
Dec 17 17:09:50 (Use `node --trace-deprecation ...` to show where the warning was created)
Dec 17 17:09:50 [INFO] [outbound] secured verified=false cipher=TLS_AES_256_GCM_SHA384 version=TLSv1.3 error=ERR_TLS_CERT_ALTNAME_INVALID cn=*.mydomain.com organization=""
[core] hook=connect plugin=dnsbl function=connect_multi params="" retval=DENY msg="host [123.456.789.012] is blacklisted by zen.spamhaus.org"