This email is most definitely a scam. In general, any email you receive that requests personal user information via email is likely to be fraudulent. This is called phishing, and it's a technique used to gain unauthorized access to your accounts.
Customers should never provide username and password information via email to anyone, even it the email looks like it is coming from your bank, credit card company, or any online account. Also, if you do receive an email from Cox that asks for personal information, please send the email as an attachment to email@example.com. Use the links below to learn more about spam, phishing, and how to send these types of email as attachments.