When you are curious, though, or asked to pass along all message headers for helping thwart spam or troubleshooting a mailing list issue, it is good to be able to uncover the lines of header information normally hidden in Mozilla Thunderbird. (Mozilla Thunderbird will show some headers — such as the sender and subject — by default, if course.)
You need not go to the full message source either to show all headers; Mozilla Thunderbird
View Complete Message Headers in Mozilla Thunderbird
To see all header lines laid out for an email in Mozilla Thunderbird:
- Open the message in the reading pane, in a new tab or in a new window.
- Select View | Headers | All from the menu.
Click the menu button first if you see no menu bar.
To return to you standard set if headers shown, select View | Headers | Normal from the menu.
If you want to see or need to copy the header lines in their original, not formatted manner, you can open the message's source in Mozilla Thunderbird and use the lies from the top until the first empty line (after which the email's text begins).
(Updated March 2013)