Try this: in the Inbox, select Accounts, Accounts..., select the name of your email account, Next your way to the 4th page, select Options, netx to Page 2/3.
Check the box for "Outgoing mail requires authentication" as well as "Use separate settings"
Outgoing Settings....
Outgoing server settings
For username use your entire email address:
your_user_name@cox.net
Enter your password
Leave the domain blank
Check the box for save password
Check the box for "Require SSL for outgoing mail"
Click OK in the upper right corner