Even more regrettably, there has been zero response from either Professor Lange, RapidMail, or the Internet service providers involved to an emailed complaint and request for clarification we sent on July 4. There has been more spam on two occasions, however, on July 1 and again today, July 30. Therefore the matter must be made public.
Update Aug 25: RapidMail responded on July 30 to say that they would contact the customer to ask about permission for some random sample addresses. We told them we were looking forward to hearing the results. Nothing since – except for more spam, so we listed 18.104.22.168/24.