Message Blocked error from mac.com address when sending personal email

Did you ever find a resolution to this? I'm running into what I think is the same situation. I have a .mac address, and my wife uses Gmail, sometimes with a custom email domain (yourhometownconsultant.com). Seems like the problem occurs most frequently with messages she is trying to forward to me. Started Apr 16th and has probably happened 15-20 times since. I looked at the link in one of the bounce messages she received (Postmaster information for iCloud Mail - Apple Support), and it suggested I contact icloudadmin@apple.com with my particulars for help, which I did, attaching copies with full raw headers of both the message she was trying to send, as well as the bounce message she received (you can get this is Gmail by clicking the three-dot menu on any email and clicking View Original and then click the link to download the original message, which will download a .eml file with the full email inside.. it's just a text file you can view in any text editor). Now hoping they reply 🤞