many legitimate senders are lazy and use "newsletter@xxxyyy.com" or some other domain
My Outlook account has received literally thousands of emails from newsletter@ accounts and 99.99% of them have been Junk Email. I found one such account from which I last received email in 2013. But, I regularly received email from that sender and could have written a "Save" rule for it. I receive 30-40 Junk Emails per day with most of them from a newsletter@ account. Outlook intercepts them with Junk Email rules before I can use an Inbox rule to block them.
If you have a contact that sends email with that address, write a higher priority rule for that account with Action "Save". You can "File into" Spam if you really want to review all the rest of them. But, Cox Spam settings would probably send them to Spam anyway, so that would defeat the purpose of the rule. (I say probably because it's been months since I've seen Spam in my Webmail account).
If Outlook had this Filter Rule capability, my Junk Email problem would be over. Webmail's Filter Rules capabilities are much better than Outlook's Rules.