When sending mail to Charter/TWC/RoadRunner domains (full list here), are you seeing any of these bounces?
- 550 5.1.0 sender rejected AUP#I-1310
- 550 5.1.0 sender rejected AUP#I-1320
- 550 5.1.0 sender rejected AUP#I-1330
These apparently correlate to the ISP's Cloudmark servers putting a sender into a rate limited "time-out" for anywhere from five minutes up to 24 hours. According to a post on Mailop from 2017, one bounce means 5 minutes, another means a one hour timeout, and the third means a 24 hour timeout. They might be listed in that order above, but I'm not sure.
Anyway, the net here is: In addition to investigating the underlying potential reputation issue (don't be a spammer, please?), you might want to slow down sending if getting the first or second error message. Perhaps throttle sending to trickle out over a number of hours instead of allowing as much mail to send as possible at any given second.
Information on dealing with Charter/Roadrunner deliverability issues is sparse (they no longer have a Postmaster site, alas), so I thought it'd be good to share this (best guess) information here with the hope that other folks will find it useful.