I'm seeing this error for all recipients on a particular domain:
"spamcop.mimecast.org Blocked - see https://www.spamcop.net/bl.shtml?198.61.254.91. - https://community.mimecast.com/docs/DOC-1369#550 [bEjCcA39P3SxsOV3CZ9qSw.us331]"
However, as you can see here, that IP is not on the blacklist: https://www.spamcop.net/w3m?action=blcheck&ip=198.61.254.91.
Here's a link to the message and headers: https://www.mail-tester.com/test-iyn5n@mail-tester.com