Hi Steven
As you mention smtp.cybernet.ch -> please provide me offlist some more details (from mail address, recipient, time) and I can grep in the mailserver logfiles to find out what happend with our black-magic vodoo filters ,-)
I'm afraid I have to apologize for suggesting that cybernet had magical skills. I have to blame myself for that one.
It seems that at least one cybernet mail server (mta02) is listed on sorbs and I found a script that was going through our mailserver's logs and null-routed ips present on blacklists and nonetheless sending high volumes of messages.
That's why I never saw the messages reaching our mailservers and why some got through and other didn't - depending on which relay they were taking.
mea culpa.
Regards
Jean-Pierre