I want to thank everyone who responded to my post. I was resolved this problem this evening with help from Cox technical support. I will summarize what fixed my problem for others.
First, I use a different Internet Service Provider (ISP) provider than Cox. Therefore, I was told that I had to use the SMTP mail server of my current ISP provider not Cox to send emails. This was the root cause issue. I changed the outgoing mail server to my current ISP in Microsoft Outlook . Now, I can send emails again with no issues. It was a 5 min solution in the hands of a very capable technical support staff member.
In summary, you have to change
"smtp.cox.net" to "smtp.your ISP's name.net"
In the Advanced Tab, I had to input in my ISP server# in the "Outgoing server (SMTP):" box,. You have to follow the instructions from your current ISP in order to set up Microsoft Outlook or any other email client properly. Mine was on their website.
For incoming mail, I continue to use the Cox incoming mail server ("pop.cox.net") in order to access my email. That's why I was continuing to receive emails with no issues. I made a suggestion to Cox to create a technical bulletin with instructions on how to handle my situation. These instructions would be helpful to Cox customers. We live in a very mobile society so it is not unusual for users to change their ISP provider due to a variety of reasons.
I apologize in advance for my explanation. I'm not a computer techie so this is my attempt to convey general information only. Hopefully, it points someone with similar issues in the right direction.
In closing, my key learning was that my outgoing mail server (SMTP) must match my Internet Service Provider's outgoing mail server.