Up until today Thunderbird (v. 102.15.1) was working well. Today I found it was not downloading messages from my email server (Zoho). I tried many things to fix it, to no avail. Finally I restored everything from a full backup I had made a day previous when Thunderbird was working well. Thunderbird *still* doesn't work. Even test messages I send to myself are not downloaded. When I click the button "Get Messages" normally it checks for and downloads all new messages. Now clicking it does nothing. If instead I click the down-arrow next to the button and choose "Get all new messages" it does check for new messages and claims to be downloading them, but they never appear in my mailbox. I have Thunderbird (admittedly, a later version) installed on another computer and that continues to work fine, so the problem doesn't appear to be caused by the server. What could be causing this behavior?