Starting a little more than a week ago, email that I send to different people all of whom have woh.rr.com email domains is never delivered. Four days after I send the emails, the Mail Delivery System sends me a message saying my email couldn't be delivered, and the reason Is "delivery retry timeout exceeded." I have no trouble sending email to anyone else. Only to people who use the TWC domain woh.rr.com. Also, the MX Toolbox test says the rr.com domain is broken.
My email service is provided by 1and1.com. Their tech support said that Spectrum has a disagreement with 1and1, and as a result, Spectrum is intentionally limiting the number of simultaneous emails it will deliver from 1and1 customers. So most emails from 1and1 don't ever get delivered.