How to View the Source of a Message in Mozilla Thunderbird

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by Heinz Tschabitscher
A former freelance contributor who has reviewed hundreds of email programs and services since 1997.
Updated September 30, 2019

Get Mozilla Thunderbird to show you the full and direct source of an email, not just its formatted text and some headers.

Why View an Email's Source?

Does an automatic wristwatch tick with greater precision if its bottom is of glass and you can see the balance wheel rotate? Does a painting look different if you can see the layers beneath the top? Does food taste better if you watched it being boiled and spiced?

How about an email and what is going on behind its scene? The source of a message may not make it display differently—it can, in fact, be very difficult to get an email's contents just from looking at the source code not interpreted and turned into legible form—, that very source can be helpful to identify the origin of spam or problems with an email message.

The source code contains a trace of the path an email took, and it contains the HTML source for an email, attachments in, possibly, Base64 encoding and hidden header lines.

In Mozilla Thunderbird, getting access to all this is easy.

View the Source of a Message in Mozilla Thunderbird (Without Opening the Email)

To display the source of a message in Mozilla Thunderbird (or Netscape and classic Mozilla):

  1. Highlight the message in the Mozilla Thunderbird message list.

  2. Select View | Message Source from the menu.

    Click the menu button or press Alt if your menu bar is hidden.

  3. That's it!

As an alternative, use the Mozilla Thunderbird menu button:

  1. Highlight the email in a list.

  2. Click the Mozilla Thunderbird menu button (≣).

  3. Select View | Message Source from the menu that has appeared.

View the Source of a Message You Are Reading in Mozilla Thunderbird

To open the source view for an email in Mozilla Thunderbird:

  1. Open the message for reading.

    ​​You can open it in the Mozilla Thunderbird reading pane, in its own window or in a separate tab.

  2. Select View | Message Source from the menu. ​​The Mozilla Thunderbird menu route also works, of course:

    ​​Click the menu button in the main window (with the email opened in the reading pane or a tab) or the message's window.

    Select View | Message Source from the menu that has shown.

  3. That's it!

View the Source of a Message in Mozilla Thunderbird Using a Keyboard Shortcut

If you dig down to the sources regularly, you can also use and remember the Netscape keyboard shortcut for this activity:

  1. Open the message (in a tab or window, or just in the reading pane) or make sure it is highlighted in the message list.

  2. Press the source viewing keyboard shortcut:

    • Ctrl + U on Windows and Linux,
    • Alt + U on Unix and
    • Command + U on a Mac.

  3. You're done!

Can I Also View Just All Header Lines (Not Including the Message Body Source)?

If you are interested just in the message's header lines and do not want to be burdened by HTML source code and MIME sections, Mozilla Thunderbird offers an alternative to displaying the complete source: you can have it display all header lines (but not the message body's source) in a formatted manner.

(Updated August 2016, tested with Mozilla 1.0, Netscape 7 and Mozilla Thunderbird 45)