Successful Email transition to Yahoo: using Thunderbird on Windows

Stickfoot63 I am sorry you are still having issues...it took me like 12 hours on and off to get it done and it seems one small thing could be different for each particular issue.  I went thru my notes that I tried to take and as I said on Yahoo webmail I did set up an App password and TB did not like it but a couple things I did when I kept getting error messages..

• I kept getting error messages that User Name failed..correction was to use full email address incl Cox.net.
• I guess has to match what Yahoo has?  Full User Name must be full email address..can’t remember what it has to match.
• Once the names were full email addresses and OAuth2 and use new Yahoo password (not app one) it worked.  Had to get out and back in a couple times and I think it asked for permission at some point.
• after I changed the IMAP/SMTP to the Yahoo settings I too got an error message saying I changed and TB had to restart..did each time. 
• I also cleared cache and history and cleared out all my saved passwords in TB.
• I also allowed cookies in Settings/PrivacyWeb  and security (read in one of my travels you had to allow cookies)  The set up of this section of TB has again changed with ver 15.11.1 so it does not look as it did before..might have nothing to do with it but worth a shot.
• It is so easy to get frustrated at something we have no choice or control about and agree Cox/Yahoo/TB could have done a better job for all the different senarios we are all experiencing.  Step back and try again another day. Good luck!