@david, would you mind having a look at the issues below, the latest update to the mail-receiver removed the ability to implement additional anti-spam measures, which worked wonders in the previous version, and my forum is under increasing spam pressure again due to the last change.
I tried to figure out what the root issue is, but I don’t have deep enough knowledge of postfix to figure it out. I found similar reports (client=unknown even when PTR record exists in DNS) regarding postfix in a chroot jail, so this might have something to do with it. Also, dnsutils seem to be missing from the new mail-receiver Debian image, but installing them still doesn’t fix the issue?