Hello sethm1,
I appreciate needing steps for successfully setting up your cox.net in Thunderbird. When using a client with Yahoo, you'll need to generate a Third Party App Password for your Cox.net account to be able to use the Outlook with your Yahoo-transitioned Cox email account. This is a requirement by Yahoo's terms.
Step 1:
Log into Yahoo mail using your PC or Mac. You will need your full cox email address [youraccountname]@cox.net and the new email password you created when you completed your Cox to Yahoo transition. Once in the Yahoo mail click the icon at the top right (your name or initials) and select "Overview". Now from the menu at the top select "Security".
Step 2:
Look on the right for "Other ways to sign in" and you will see "App Password - If you don’t normally use a password to sign in to your Yahoo account, here’s where you can generate a password for 3rd-party apps that require passwords." Click on "Generate an app password" and provide a name for the app (e.g., Mac Mail or iPhone Mail). Yahoo will provide a new password for the Apple Mail app - make a copy of it (don't include the spaces).
Step 3:
Name - Your name
Email - [youraccountname]@cox.net
Description - what ever you want displayed
Incoming Mail Server
Host Name - imap.mail.yahoo.com
User Name - [youraccountname]@cox.net
Password - ** see note below
Outgoing Mail Server
Host Name - smtp.mail.yahoo.com
User Name - [youraccountname]@cox.net
Password - ** see note below
Use SSL - On
Authentication - Password
Server Port - 465
**Now carefully type in the new password generated by Yahoo and press return on the screen keyboard. You should get checkmarks indicating success. You need to do this for both the Incoming and Outgoing Server settings.
These steps should help you out, as these steps were confirmed to work for others when setting up the account after the transition to Yahoo.