Get Email Headers in Outlook Web in a Chrome Extension

I’m working on a project where I want to process email headers. My organization uses Outlook Web. I’m designing a browser (chrome) extension to process headers of a email that user receives. I’m more interested in the Recipients of the email (To, Cc, Bcc)

An email looks like:
enter image description here

On Inspecting the page, I see the following:

enter image description here
which shows only what is displayed on the screen, not all the recipients.

The email header is showed when user clicks the down arrow to the right of Reply all and then clicks View Message Details. Then a popup box open with the email header which also has the Recipients in To and Cc.

How do I get the header (importantly To and Cc) of the email using chrome extension?