Content match on email header info

I am trying to rename email messages saved as .eml files in the format yyyy-mm-dd hh:mm:ss - Sender - Subject. I am using content matching to extract the required information. It is all available in the email header, but Hazel does not seem to be able to read it. Hazel will only match content that appears within the body of the email message. It will find the date of a quoted message if the quote includes it, but not the actual current message. Is there a trick that I am missing?

I don't think the header is any different than the content in this regard. Hazel just sees text. Testing it out here seems to confirm it. If you are having problems matching, I suggest focusing on your patterns. If you email me your rule and an example email where it isn't matching, I can take a closer look at it.