Really I thought cox sent instructions for that. My understanding is there is something you need to do with Cox to accept the transference. But as a non Cox customer living about as far from Atlanta as it is possible to be and still be on the same planet, it is only an understanding.

Is you current cox account IMAP or POP? It is the first thing on the pane in account settings > server settings.

Matt, Thanks for trying. We have Cox Complete Care and talked to an agent Saturday night. She couldn't figure out how to connect us since Thunderbird is not showing as one of the options to import. She suggested we contact Yahoo, which my husband had already tried, waited an hour to get an agent, and then the agent didn't help him. We've already been transferred out of our Cox account and there is no Account Settings button on the Yahoo page.

This official link has all the info. It doesn't explicity speak to Thunderbird, but to 3rd party clients and shows POP and IMAP. https://www.cox.com/residential/support/coxnet-email-transitioning-to-yahoo.html

David, The information you sent was helpful but I'm not there yet. My Yahoo mail is not coming in through Thunderbird. The article told me: "After completing the steps, you will then need to set up your email address again via your preferred email client with Yahoo settings or use Yahoo webmail." I checked Thunderbird settings and they are exactly what Yahoo specifies for incoming and outgoing mail. I went to the Thunderbird web site to re-enter my email address and got a message that I already have an account with that email address. It seems like Thunderbird is compatible with Yahoo but I can't get the two to work together.

Well, then post screenshots of incoming and outgoing servers. You also needed an app password, not your regular password for web access.

Last night Yahoo support got Thunderbird to serve as a third party client. She sent two test emails to me to make sure it was working and it was. After her remote session was over, I sent an email. However, today my emails won't send. I get an error message to check my smpt settings. I enter the email that is listed for my Yahoo account and I still get the error message. I've tried changing the authentication method from normal password to no authentication but messages still won't send.

Please post your Troubleshooting Information. At the top right of the Thunderbird window, click the menu button ≡, then select Help > More Troubleshooting Information. Press the "Copy text to clipboard button" and paste the information into your reply.