Pegasus

Inside the Pegasus Inbox double-click on the email message to open it.
The email will open in new window, and a new menu will appear.
On the new menu select the Raw View tab to show the entire non-formatted email message.
Using the mouse, click and highlight the header text, then copy it to the clipboard by right-clicking and selecting Copy.
You can now paste it into an email by creating a new email, right-clicking the mouse, and selecting Paste.