Just pick any email, newsletter for example and resend it from external email address, like Gmail.
Then go to proxmox, Administration > Tracking Center and search for that email, and all spamassassin scores will be in pmg-smtp-filter line.
Would be a great improvement of PMG, if not only in the receiver and sender details for each address it would be possible to have an insight of the scores/messages behind but also in this statistic to be able to click through to the message list.