Whilst I don't use Outlook, it might help if you show your filter details for blocking the .tk top level domain. Anyone using Outlook can check it and confirm if it is correct or if it is even possible to block a top level domain.
I would also suggest that you modify your first post (Modify button in the post) and add Outlook into the subject.
You also don't say what avast version you are using and if this is at all related to avast (e.g. where you trying to add this block) and its anti-spam module in the AIS/Pro version or is only to do with Outlook.