This is fixed - one of our groups had a sender address which was not setup correctly in office365. This was the reason I started this topic.
The question here is how can I reset zammad to not show a wrong health status as the original problem is fixed and all emails are sent without any errors?
I did not need to delete the job - 24 hours later based on the timestamp in the Job, the system solved the system by itself and monitoring is now green. This is now the new status of the Job:
zammad run rails r “p Ticket::Article.find(21482).preferences”
{“email_address_id”=>12, “delivery_retry”=>18, “delivery_channel_id”=>5, “delivery_status”=>“success”, “delivery_status_message”=>nil, “delivery_status_date”=>Sat, 23 Mar 2019 08:08:49 UTC +00:00}
The topic can be closed - Thank you very much for the great support.