Similar issues for family members using Windows 10 and XP. One person using XP and Outlook 2003 keeps getting prompted to enter their Cox mail password to receive/send or they get an Internet Security windows about Cox trusted servers. Clicking YES removes this until the next time which is intermittent.
Another person using Windows 10 and its Mail client has issues sending email. Sometimes it works - sometimes the mail sits in the Outgoing box. Cox points the finger at Microsoft and I'm sure Microsoft will point the finger at Cox.
Server settings for the XP person are:
pop.cox.net - port 995, smtp.cox.net - port 465 (with SSL set on for both)
Server settings for the Windows 10 person are:
imap.cox.net:993:1 (port and SSL on), smtp.cox.net:465:1 (port and SSL on)
UPDATE: Changed the smtp.cox.net port to 587 SSL enabled on both family member's email clients. Will try out and see what happens. Tests for outgoing/incoming from non-Cox email addresses were successful, but I'm not convinced this is a permanent fix.