I took a look into overviews and the configuration of them.
Right now there doesn’t seem to be a filter or hook for that.
This might be useful as Feature Request if needed.
A problem I see is that inline pictures are an attachment, too, and could actually draw those filters useless.
E.g. when you have an inline image inside your signature that you always sent on your E-Mail. Every E-Mail may look like an E-Mail that has an attachment.
Let me know what you think and of course always feel free to submit Feature Requests here.