552 5.2.0 bounce error sending group emails!

I got on this Cox Forum for one reason - to let other people know that I am experiencing the same thing they are - I cannot send out group emails anymore as of January 25th, 2018. Every Cox tech told me something different when I called for help. I can send only 9 recipient emails out. One tech told me to buy more expensive speed. Now I wonder about that. My friend who uses a Lap Top couldn't send his group email out from my house over my WiFi but could do it at his house where he pays for fast Cox service. Another tech told me to get Gmail. I use a home PC only. I did get Gmail, and it works to send out my Group email to 80 recipients. For the past few weeks I've been sending 9 out at a time to my 80 recipients. What a pain! Your Tier-2 guy said Cox really does want to get out of the email address business and just be an ISP provider, hence his suggestion to get Gmail.