After some more tests with orders I found out, that a testfilter in my own account successfully copies the incoming mail to public/webseite folder while the filter in the “archiv” user did not.
My account has “Full Access” set to this public folder in the GUI, user “archiv” has “read/write”
This translates to:
doveadm acl get -u archiv Public/Webseite
user=archiv create insert lookup read write write-deleted write-seen
user=spielhagen admin create delete expunge insert lookup post read write write-deleted write-seen
So I gave “archiv” “Full Access” in the GUI and now it works, “archiv” successfully copies incoming messages to this public folder when the filter triggers.
Thank you Markus for taking me by the hand and not letting me give up on this.
Uwe