The Whonix devel maling list has been getting this kind of spam detection for quiet a while:
Spam detection software, running on the system “whonix.org”,
has identified this incoming email as possible spam. The original
message has been attached to this so you can view it or label
similar future email. If you have any questions, see
@@CONTACT_ADDRESS@@ for details.
The problem is not urgent since we can still see emails from the attachments. But it is better if there is a way to fix it.
Maybe white-listing all the emails sent from blackhole at torproject dot org?