News: They are not "too big" to be held accountable
We've identified a wealth of IP addresses from very reputable services which are allowing themselves to be abused by attackers to effectively DOS attack a handful of our clients, flooding their inboxes with spam for malicious purposes. These include such big names as OVH, Sendgrid, Amazon, Google, and Mailchimp. At one point we refused to blacklist IP addresses of large providers as this can prevent other clients from receiving legitimate email. However, all of us together (that's you, our customers) are too large and influential combined to be bullied around by these companies who care more about their bottom line than the wellbeing of their neighbors.
Effective immediately, any IP address involved in these attacks against our customers will be blacklisted. Their removal can be requested after they've played nicely for a bit. We won't remove them in the middle of them flooding one of our customers, but we won't list them permanently either. We think that's fair, and we feel like our customers agree. You've entrusted us to protect you and operate as a collective which seeks to make the email landscape better for everyone, and that's what we do every day.
Update 9/10/2021 - The temp list which was most likely to contain IP addresses from large brands has now been cleared from our blacklist following 24 hours of good behavior. Any remaining IPs that are blacklisted are jobs for the owners of those IP addresses. It is their job to keep them clean, not yours. Direct all of your complaints to them, they can request removal when they've resolved the problem that appears when they search their IP at mxrbl.com.