Solved
The connection to smtp.cox.net failed !??!
My "transition" from Cox to Yahoo was working yesterday. But today when I try to send email from Windows 10 Outlook as well as myemail.cox.net webmail, I get this: Cannot Send Mail. The connection...
I may have made a mistake and changed the Outlook SMTP port to be identical to 465, in both Outlook as well as iPhone smtp.cox.net server port instead of the preferred port 587. Not sure which is required but 587 for iPhone, but 465 for Outlook works now.
