Hello Martin,
I've just received this statement to the swisscom pwlan blacklist problem which I've reported earlier to this list. AFAIK there is no easy solution to this problem and to avoid false positives in the spam-scanning prozess.
Any creative ideas how to solve this ?
Well, it's not very creative but I think it's common sense, that if you cannot trust the users sending mail through your mailserver you have a situation comparable to an open-relay server - moreover if Swisscom claims it cannot find the responsible users ("da wir die Verursacher der Spam-Mails nicht eruieren und herausfiltern können").
In this case they have to either require every user who wishes to send mail through their servers to authenticate so they can track the people down when something happens or they have to close relaying completely and ask their users to use a mailserver responsible for their mail address' domain.
Jean-Pierre