Hello, I had same problem and am an apple phone user. The yahoo support phone number is disconnected and have to pay for phone support now. I was able to get assistance from cox support and is super easy fix. On iphone go to Settings, select Mail app, select Accounts, select the Cox account and then select Delete Account. After doing this I can now receive and send email under the Yahoo account on Apple Mail.
This has been a disaster. It took me more than an hour to get the yahoo to work through Mac Mail on my desktop. I could then receive emails, but not send, on both my iPhone and iPad. The solution by gbru allowed my iPad to send, at the cost of losing all the emails that were on my iPad when the account was deleted. It did not work on my iPhone. This sucks. Cox should have made this a lot easier. "If you like your doctor, you can keep your doctor...."
This solution worked perfectly for me. Thank you. Hadn't realized I kept the other account. IOS seems to fall back to that for sending.
