It was working flawlessy in Win, but I needed to switch to a mac, so I copied the Profile folder and set it up as default using the Profile Manager. I have two gmail accounts which seems to work when asking password via OAuth2, but after authorizing i get the message about authorization failed while connecting to IMAP server. Other two accounts are old POP3 account which always worked under Thunderbird. They too keep asking for the password and are unable to retrieve the emails. I set up a gmail account in the default Mail app, and it works fine. So the problem is specific to Thunderbird, but I am unable to locate it. I switched on the option on gmail to allow the connection to less secure apps, but nothing changed. I have already tried this: https://support.mozilla.org/en-US/questions/1275293 but nothing changed I have turned off MacOS firewall, but nothing changed. Is there anything else I could try? For example, is there a way to get an error log of the failed connection?