552 5.2.0 bounce error sending group emails!

Nice find, john2222!  Very interesting.  I get Cox's "don't look behind the curtain" approach, though.  You publish your parameters and every "spammer" is going to know how to fly under the radar.  I'm sure that's the logic.  Only makes sense.  My problem is that there is no human, but a robot, pulling the levers behind the curtains.  And the robot is using a machete, not a scalpel.  Robots can't say, "Oh!  Church choir. Not spam." or, "Oh! Little League baseball team. Not spam."  You know, the way 'normal' people use email.  And, no, I am not recommending Cox hire a bunch of humans to start looking at email.  Cost prohibitive and invasive.  I'm just saying stop swinging the machete, for cryin' out loud.  You are lopping off the hand that feeds you!  Be reasonable.  Like the vast majority of ISPs you point out in that link.  Are they all getting blacklisted?  I'm thinking not.

Hopefully a Forum Moderator will drop by as you have asked.  My guess is, though, their hands are tied and they will give you all the fudge/hedge lingo here:

https://www.cox.com/aboutus/policies/speeds-and-data-plans.html?sc_id=cr_gov_red_z_policy-limitations.asp_vanity

That's the party line.  We can argue the wisdom of it all day long.  Regrettably, they hold all the trump cards.  For people who do not have any ISP choice in their locales, that really, really stinks.