Servers: smtp.us.opalstack.com
Fixed - The US SMTP is no longer blacklisted. (21:59 UTC — Jan 5)
smtp.us.opalstack.com is currently on the Cloudmark blacklist which is used by Comcast and other services. We’ve submitted a delisting request to Cloudmark and are waiting for a followup from them. (15:42 UTC — Jan 5)