Problem consists longer than a year with recurring messages: "Server.imap.mail.yahoo.com has disconnected. The server may have gone down or there may be a network problem." I am able to send/receive some messages, but accessing (sub)folders does not always work or changes (e.g. moving files) don't seem to get through. Any idea for the reason of this error message and suggestions which settings I need to change? After trying for so long to fix it, I am stumped. Settings: Lenovo Thinkpad X1Gen2; Windows10, current TB version 91.4.1; VPN (PIA) setup split tunnel excluding TB from VPN (Problem occurs with and without VPN activation. PIA whitelisted yahoo account just to be sure.) Issues does not occur with other email accounts (e.g. gmail, etc.) nor with other programs e.g. Bluemail (which I really do not like using and am thus hoping for a fix for TB), taken together doubting (not excluding) network problems (ethernet, wifi). Implemented instructions in https://support.mozilla.org/en-US/kb/thunderbird-and-yahoo. i.e. Privacy/Security/accept cookies and SSL/TLS/OAuth2 settings, etc.