Well, it's been a trying few days. I've been with Cox since 2003, and had a few e-mail issues over the years, but this change has caused me to be unable to send e-mails via Eudora (yes, I still use version 7.0) via Cox.net since the morning of January 25th. I followed the instructions found here online and they do NOT work. So, since I get my e-mail from g-mail, I was told I could send it through them too. BUT, it wasn't working for some reason. So... I spent much of today googling to find the problem, and low and behold I found a link with an issue another guy had very similar to mine...
https://www.justanswer.com/email/9lbwt-i-m-using-eudora-7-1-0-9-access-mail-gmail-pop.html
If you scan that thread, you will be a link that says the following...
Since Eudora is an older client you have to access your gmail account via a browser and then allow less secure apps using this link https://www.google.com/settings/security/lesssecureapps
I clicked that link to lower my security and then set my Eudora to send e-mail via G-Mail and BOOM, it worked!
Hopefully, this little tidbit will help out others in my situation. I must say the tech support here at Cox.net is lacking. Bottom Line: Do it yourself via Googling worked for me, so perhaps it will work for others!
Good luck to all still working to solve the issue!