Outgoing smtp login problem
First the smtp.cox.net vs smtp.cox.net shouldn't matter. Both should work.
Second I would check your account and see if you maybe have a extra smtp entry that has incorrect info. That might explain why it sends but gives you the error both.
Third you just want to use your username in general but why are you even using username and password for smtp (outbound) mail? Are you sending from outside cox's network? Try no authentication on outbound on port 25. See if that works.