An email is sent to the junk folder again after marking it 'not junk'
An email from "romi.gov" (a legit email from the city of Royal Oak, MI) is sent to the junk folder. I mark it "not junk", it moves to the inbox, and then is sent back to the junk folder. My email provider is xfinity. It's an imap server. They seem to stay in sync, but it seems that whether Thunderbird marks it as junk is independent of xfinity, which may then also call it junk. I'm not sure who follows whom.
Alle svar (1)
You email provider is Yahoo and they know better than you. They decide what is junk. Your only hope is to add the sending address to the online address book maintained on your providers web server because Yahoo offer no opt out for their spam tools.
There were issues with older Thunderbird versions not playing well with the way yahoo mark SPAM as SPAM, but they were fixed some years ago now. I have not seen a rash of people with similar issues as you so I am guessing if that bug affects you, you need a new version of Thunderbird. The current release is 91.5.1 if you are looking to confirm if you need an update, help menu > about shows the release version you are running.