Emails not received to Comcast addresses in mass distro list

I am writing to request assistance with a rate throttling issue we are experiencing when sending emails to Comcast.net addresses from our domains (unh.edu, usnh.edu, keene.edu, plymouth.edu, and law.unh.edu). Our email relays are 132.177.152.195 and 132.177.152.196. We have encountered rate limiting (e.g., RL000003) which is impacting our email delivery.