Email: How to extract a piece of raw message body or references (header) or in-reply-to header?

I have a rule that injects a tracking pixel into a newly created email message and adds References into the email’s header with an UUID of the tracked message.

But I’ve found no means of actually grabbing these values neither through filters nor through the Fibery rules… One of the bigger needs is to link my entity in CRM/Person Email Activity to the related entity in Email/Email.

When I use filter “Message (snippet)” in Email/Email while trying to find an injected pixel link, it cannot find it, although the link is there according to Gmail’s > Show Original.

How do I retrieve the value of the References header and/or check right inside Fibery if the link is present in the message body and/or retrieve the value of In-Reply-To header?

Am I missing something here?

Thank you.