Somehow an important email address of a client ended up in the sieve blacklist and it was deleted.
I have decided to go back to courier. Changing a few dozen of servers again after a few weeks is a hell of a job, but hey, thats what weekends are for.
I am sure someone, somewhere found sieve a good idea, but in reality i find it not working. One miss-click in webmail and important emails are gone in every client because they are from then on deleted at server level.
regards
Jan