Want an easy way to see mail headers in Mail.app? They’ll pop right up, and I promise you’ll like it.
I found this by accident, and it is useful so I thought I would share it. My fingers are used to pressing command-option-u to “view source” in browsers on my Mac. I was context-switched to Mail.app today when I tried viewing source on a web page, and what do you know? A window pops up with the html source of the selected email message. You can also view the headers in situ in the mail message, by pressing command-shift-h, if that is your preference.
Good to know, good to know.