I keep getting emails saying my inactive cox.net email will deleted.

Do you have access to the email account in question? If so, log into it and it will no longer be inactive. If you don't want the account, delete it manually. Just remember, once gone, you will no longer get it or any new Cox email account. 

Have you moved recently, or do you recognize the email addresses that say they are inactive? It could be an address that a family member used, OR if you have moved recently, then Cox may need to transfer the email addresses from your previous physical address account to the NEW physical address account.