Successful COX to Yahoo email transition with Thunderbird
Before you start the transition, it is useful to have a separate email from another provider for testing purposes since once you start the process there is no going back and nothing will be working for a awhile. When I got the ready to go email from cox I assumed it would be days before the service would stop. My cox accounts stopped working the next day, so get on with it already.
On my PC I had Thunderbird as my POP email client and wanted to keep this. I like having my emails stored locally where they can easily be backed up. I initiated the email account transition on the yahoo mail page by entering the existing cox email address, password and generating a new yahoo password. The birthday you enter can be anything but it can't be changed later. Write everything down.
This created a new yahoo email account with the old cox address. I was able to use the Yahoo webmail interface to access the new account, and immediately received emails from yahoo. I tested sending and receiving with my 3rd party email, and after some delay these initial emails went through also. I was able to edit my default first name, last name and preferred name on the yahoo account personal info page. So much for webmail.
To get Thunderbird working I was able change my existing POP and SMTP server settings without deleting or creating a new account:
pop.cox.net -> pop.mail.yahoo.com , (SSL/TLS and port 995 unchanged)
smtp.cox.net -> smtp.mail.yahoo.com, (SSL/TLS and port 465 unchanged)
In these same tbird dialogs, my old cox username had not included the '@cox.net', so I added that (two places).
My existing password authentication setting didn't work when using the new yahoo password, so I changed both pop and smtp authentication to OAuth2.
Once I did the yahoo password dialog popped up and I completed the login and connected with the yahoo servers.
Still some things to tailor but basic email with tbird is working.