Yes, these are bounceback messages from Cox servers. An admin creates the rules, sometimes using well-known abbreviations, sometimes not. NDR is well-known; however, MJ is local to Cox and not well-known..
I don't know the Cox URL-policy for email because I always find an innocuous email from our HOA in my Spam folder. Perhaps Cox flags 'em as spam because the HOA includes lots of SMTP addresses as contact info within the text.
However, this wouldn't be the same problem because Cox still delivered the email to my account, albeit my Spam folder. I'm just implying Cox spam-rules for links is unclear. We'd need to see your intended URL to decipher.
AUP = Acceptable Use Policy CXS = Cox NDR = Non-Delivery Receipt MJ = (A Cox admin must have created this code but means suspicious account blocked)
You shouldn't have to do this because it's ridiculous to camouflage a URL, but how about a URL Shortener tool? I'd probably be quicker than breaking up and testing deliveries.