Hi Beverlyk,
Use the steps at https://www.cox.com/residential/support/changing-your-email-server-settings-for-microsoft-outlook-2007-2016.html to review your incoming and outgoing server settings. On the Outgoing Server tab, is "Use the same settings as my incoming mail server" selected? If so, change the setting to "Log on using" and type in your Cox Username (everything before the @ sign in your email address) and password. Put a checkmark in the box to remember the password. Then click OK. Close Outlook completely, and then reopen. Changing this one setting has worked for some folks.