Sending mail with primary account.

I can receive and send email on my two secondary account with no problem. However, I can not send email on my primary account. This problem is only with windows 10 and is present in both Mail and Mailbird.  COX just will not authentic the primary account on the Window 10 system.  My Windows 7 computer and my android phone have no problems with the primary account. Something must be wrong with windows 10? Any ideas?  The ports and security settings are the same on all accounts.