Hi Johntc,
Listen my friend, this is not a Microsoft issue, all these problems started when Cox changed the e-mail ports for security to make us safer but it has caused a whole bunch of problems. I have tried Microsoft Outlook 2016, Thunderbird, Microsoft Mail, Windows Live Mail and I get the same results on all. In addition to my Windows 10 machine I also tried it on my Apple iPad Air and iPhone 7Plus and got the same results there so you can tell them it is not a Microsoft issue. Like I said in my previous post above I worked with several Cox customer service reps and got different answers and some were not even aware of this issue. I can at least send emails and receive but I send group e-mails and I learned from another customer posted above that she was told that they are now limiting the number of people you can have in your groups to 9 people and I have 90 people in some of my groups so I would have to make 9 different groups and send out an e-mail nine different times. This is the second thing they have taken from me the first was the space they used to provide for a web site but they are not going down on their price. I worked in the IT and Telecomminucations field for like 40 years and if we changed to new systems or software we always had a contingency plan to go back to the old system if our customers experienced issues like we are having but I guess they don't care about the customer. I really think they don't have the infrastructure to support their load and they are cutting back on what they originally offered and don't have sufficient staff to deal with the demand. So I am starting to look elsewhere. Hope this helps you.
Ron