Shows the email content in HTML text or as a chat view of the conversation.
Click the three dots under the email icon to show all headers including CC, BCC and labels headers, or right click it to show the email header menu.
With the email header menu you can choose to color the email, show or export the MIME content and show the internal properties of the email.
The email header icons show the attributes of the email and in compose mode allow you to modify the attributes of the email when creating a new email.
The headers are shown below with their meanings listed