Hi Franco and Swinogers
Posting on SWINOG does seem to accelerate problem solving sometimes :-)
Swisscom has contacted our customer, explained and solved the issue.
Apparently the installed a new anti-spam measure short time ago (I don't know if cloudmark is involved).
They count the number of email to invalid recipients from an ip address. Over a certain threshold, the sending ip address is blacklisted internally.
So if a business customer is sending a newsletter to it's customers and in the past did not really bother to unsubscribe bouncing recipients, he is at risk getting blacklisted @ bluewin.
-BenoƮt Panizzon-