Update 04/05/2021 18:09 PM 22 hrs
One of the IP addresses in our outbound grid (126.96.36.199) has been listed in SpamCop RBL.. This is rather unusual for a number of reasons, but the IP address delisting has been completed. The IP address was removed from the rotation so it doesn't inconvenience the existing clients (as many places have SpamCop listed IP addresses set to bounce).
We are still investigating the original issue that caused the listing.