At the end of August we heard from Cloudmark that, “Due to the IP [of server NC036] being located in the Netherlands, it was automatically put into a lower sending class. The sending class has been increased so deliverability will improve.” Since that time it appears that emails to shaw.ca and a few other domains using Cloudmark have been delivered without delay.
If this situation continues, it’s yet another example of what can be achieved if Internet companies work together, rather than ignoring each other.