I'm the one that started this thread and am glad so many other people had the same problem - lots of good comments.
Hopefully Cox can resolve this issue. Meanwhile I will not use Cox - am using gmail that has no restrictions. Since I'm not using Cox and if there is not a fix to this problem I may think about getting rid of Cox altogether - internet, phone, cable, etc.
My problem was sending outgoing emails to multiple addressees. Not feasible or efficient to limit addressees to 9 people. I run a Pop Warner program locally, state board, etc. with over 250 families and over 70 coaches that I do send routine emails.
I use Thunderbird, release 52.6.0 as my email client - it is up to date and I do not want to stop using it as I have all my contacts, saved folders, etc. for years. Using Cox Webmail is not an option.
My outgoing server setting are correct using POP.
As I said, hopefully Cox can fix this or they will lose a lot of customers!
Tina