Thank you for your quick reply! The email admin at the company is saying that no one at their company is receiving our email newsletter — I confirmed it in our error logs (see attached). I'm not sure what you mean by this.
I'm seeing this error for all recipients on a particular domain: "spamcop.mimecast.org Blocked - see https://www.spamcop.net/bl.shtml?188.8.131.52. - 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=184.108.40.206. Here's a link to the message and headers: https://firstname.lastname@example.org