RE: Remove / Filter certain email address from Timeline
Hi Martin,
If you are using Send Email step and if the email is generated from template, you will only get the regarding field when you click on Set Props. I see your point that you are not able to set the lookup in the screen.
You could still achieve this using the following steps.
01. Create a case lookup field on email

02. Create a workflow that triggers on email create, and check if the email is notification email (you could rely on subject i assume). If the email is notification email, you can clear the regarding field and set the case lookup field instead

Screenshot below shows how you can clear regarding and set the case lookup instead by copying the current regarding

Note : Making it a real-time workflow makes it to trigger instantly - before email sent by Server Side Sync
Update : Please update the condition to only work for case entity, please see below
