We posted as much here as soon as one of my clients brought it to my attention.
Thanks for your warning; I do appreciate it.
Note that we saw no advance warning from them or we could have made changes and announcements earlier.
When we got to our server we found that only a small amount of email was blocked; I don't understand the behavior.
I do understand we need blocklists, and using what are called rhs (right-hand-side) blocklists are more effective than relying on spam assassin because someone else has searched through the messages.
In case anyone isn't sure, what rhs blocklists do, is block spam from senders who send out email with known spam/junk links in them.
Jeff