It appears that the OVH team has worked with Spamhaus to remove the false positive that was affecting email20
We expect OVH to contact spamhaus directly today. For the short term, we have changed the outgoing IP address of exim on email20, the new IP address isn't blacklisted & will resolve the spamhaus block. Once the block has been removed on the original IP, we will revert to using that IP.
In the afternoon of Dec. 10, our monitoring system noticed a spamhaus block on the email20.wpcloud.ca cluster. We contacted spamhaus directly & were informed that their system has blocked an entire range belonging to OVH, the datacentre where email20 is located. This data centre is the largest in Canada & the third largest in the World. For spamhaus to block an entire IP range is extreme & we expect that to be resolved quickly.
Please note that this is out of our control, spamhaus, which is a mostly automated system has obviously mistakenly blocked an entire IP range.
We have been in contact with both parties & expect action. If you are affected, we would encourage you to contact spamhaus.org directly, as they are the organization that has decided to block your emails, on an email server that isn't sending spam & is highly filtered.