Just in case somebody is annoyed and wants to automaticly move mails fed to the mailinglist via HyperKitty to go to trash, this is how it works:
kmail -> settings -> filter
- add a new filter - set rule in left dropdown list to "header contains" and the text field in the right to "User-Agent: HyperKitty on https://mail.trinitydesktop.org/" - set "action" to "move to trash"
move this filter at the top of the filter list and be happy :)
Nik