While moving old SENT emails on my computer, I notice that I can receive email envelops, but can no longer open them and cannot read the message. ERROR MESSAGE: SERVER IMAP.FUSE.NET HAS DISCONNECTED. THE SERVER MAY HAVE GONE DOWN OR THERE MAY BE A NETWORK PROBLEM. I am using THUNDERBIRD version 60.3.1 On my wife's identical computer and setup, I can open the received envelops. I did a computer restart, a THUNDERBIRD restart, and I uninstalled THUNDERBIRD and downloaded a new copy. None of this solved my problem.