421 4.2.0 sender rejected AUP#SNDR

Finally talked to an engineer (Dan) that is familiar with the spam filtering they do. (I thought I commented this before here, but I don't see it, so... I learned that the domain sending the "sender rejected" error [cloudfilter.net] is owned by markmonitor.com, which is the company that must have been contracted out by T-Mobile to do spam filtering.)

Dan said that he was already familiar with this issue because he is handling the same exact issue for another customer. And apparently he doesn't have the capability of solving the issue directly. He created a ticket for the appropriate team to try and resolve the issue and said he would call me back.

I have 2 gmail accounts (one for my home automations that is blocked by markmonitor and one that I use as my primary email). I noted that if I send emails from my primary account, *sometimes* those messages get through and sometimes they're blocked. The other account however hasn't gotten a message through since 2 weeks ago and I checked that account for "sender rejected" error bouncebacks. I have 142 such bounceback errors. That's about 10-12 messages per day on average over the past 13 days (though I don't know if any of those bouncebacks are repeated - I don't think so - each one is maybe the 3rd bounce-backs in a series of temporary delays that ends in the "sender rejected" error).

Dan said that it could take 24 hours for the spam team to address my issue. I guess we'll find out...