Login to server Mail.acsalaska.net with username napavalley@acsalaska.net failed

Please quote all error messages you see, verbatim and in full, or post screen shots of them.

Does web mail work?

First thing to do is to verify that your email server settings are correct. Here's Alaska Communications' help page on the subject (look for "Email Server Settings"):

https://www.alaskacommunications.com/Support/Email

It might help to delete any saved passwords for this account (see <Settings | Privacy & Security | Passwords | Saved Passwords>

AND

delete any cookies for this account (see <Settings | Privacy & Security | Web Content | Show Cookies>. Also, confirm that "Accept cookies" is enabled.

You should now be prompted again for your logon credentials and hopefully they will be accepted.

The only message shown is: Login to server Mail.acsalaska.net with username napavalley@acsalaska.net failed. It repeats continually. Web mail works. Thunderbird was working fine when I logged on this morning. Then suddenly the error message shows up and hasn't stopped for 4hrs. Nothing has been changed on the desktop. I just logged back in and now is working with nothing done by me. Sigh. Thank you for the info