Get a detailed log of all Thunderbird network traffic

Martin Brinkmann
Dec 7, 2013
Email, Thunderbird

If you are using the Thunderbird email desktop client on your system, you may have noticed that it does not really reveal a lot about connections that it makes.

While you do see when it is retrieving or sending emails, only the email address used for the operation is displayed, while connections to mail servers are not.

The only other information that you have access to by default are the email headers that you can display to inspect one particular message in detail.

If you want more information, then your only bet until now was to monitor your computer's firewall or use another network traffic monitoring software to do so.

The TBTracer extension for Thunderbird changes this, as it is adding network traffic information directly to the application.

The first thing that you need to do after installation is to open the options of the extension, by selecting Tools > Add-ons, and clicking on the options button next to TBTracer.

Monitor Thunderbird network traffic

Here you need to set the environment variables and restart the email client after they have been found.

Once that is out of the way, you can load the monitoring window with a click on Tools > TBTracer.

tbtracer thunderbird connections

The extension captures http, imap, pop3, smtp and nntp connections by default and displays them as they happen in the monitoring window. You can disable some protocols in the preferences if you want to reduce the amount of data displayed by the extension.

I highly recommend that you open the styles tab in the options as well and modify them as you see fit, as some default styles make the output hard to read (especially http connections with their shadow effect).

You can hit the stop button in the tracing interface at any time to stop the recording to the log. This can be useful to investigate events without having to cope with new data flooding the window.

Here you can also use the search at the top to filter results. If you are interested to find out more about a particular email address, connection type or other connection, then you can use it to make sure that only it is displayed in the window.

The one thing that is problematic here is that there are no scrollbars. You can -- and should -- enable them in the options under general, as you are left with navigating the window with the keyboard otherwise which is not as precise as using the mouse.

The extension ignores mail attachments by default. If you want them included, open the attachments tab in the interface and change the preference from "leave alone" to "decode and feed to renderer".

Other preferences that you may find useful are to show POST data and HTTP response data, include gzip content-encoding in the log output, or to block the extension from updating when it is not displayed.


It can be quite useful to monitor network traffic in Thunderbird. It is useful for extension developers for example, but also for security conscious users who want to check the connections the email client makes from time to time to make sure that it has not been tampered with.

Now Read: Change the font of emails in Thunderbird


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  1. JMGG said on January 19, 2012 at 8:25 am

    You said that Outlook isn’t your main email client, so which is your main one?

    1. BalaC said on January 19, 2012 at 9:42 am

      I think its thunderbird

    2. Martin Brinkmann said on January 19, 2012 at 10:15 am

      It is Mozilla Thunderbird.

  2. Salaam said on September 24, 2012 at 9:52 pm

    Awesome! This actually solved my problem… what a stupid bug.

  3. Claud said on December 19, 2012 at 2:08 am

    If this is the same bug that I’ve encountered, there may be another fix: (1) hover over open Outlook item in Taskbar, cursor up to hover over Outlook window item, and right-click; (2) this should give you Restore / Move / Size / Minimize / Maximize — choose Move or Size; (3) use your cursor keys, going arbitrarily N/S/E/W, to try to move or size the Outlook window back into view. Basically, the app behaves as though it were open in a 0x0 window, or at a location that’s offscreen, and this will frequently work to resize and/or move the window. Don’t forget to close while resized/moved, so that Outlook remembers the size/position for next time.

    1. Lynda said on February 12, 2013 at 3:37 pm

      THANK YOU Claude!!! I could get the main window to launch but could not get any other message window to show on the desktop. You are my hero!!!!

    2. Chad said on November 20, 2018 at 4:24 pm

      Solved my issue! 6 years later and this is still problem…

    3. Ivan X said on January 21, 2021 at 4:50 pm

      Fantastic. Thank you. Size did the trick.

  4. Andrew said on October 26, 2013 at 7:06 am

    This solved my Outlook problem, too. Thank you. :)

  5. Charles said on December 7, 2013 at 7:23 pm

    Thank you so much, this started happening to me today and was causing big problems. You are a life saver, I hope I can help you in some way some day.

  6. garth said on November 7, 2014 at 7:13 pm

    You are a god – thank you!

  7. Faisal said on February 9, 2015 at 10:09 am

    thanks a lot…. work like charm.. :-)

  8. Simon said on March 24, 2015 at 11:36 pm

    Yah…thanks Claude. I’ve been having the same problem and tried all the suggestions…your solution was the answer. It had resized itself to a 0/0 box. Cheers

  9. Olu said on April 14, 2015 at 1:35 pm

    Excellent post. This had me baffled even trying to accurately describe the problem. This fixed it for me.
    Thank you

  10. Coenig said on July 23, 2015 at 7:36 am

    Thanks a lot for the article. Don’t know why it happenend, don’t know how it got fixed, but it was really annoying and now it works :-)

  11. Fali said on January 20, 2016 at 4:19 pm

    Thanks a lot. I was facing this issue from past 3 week. I tried everything but no resolution. The issue was happening intermittently and mainly when I was changing the display of screen ( as i use 2 monitors). The only option i had was to do system restore. But thanks to you.

    1. MIki said on January 10, 2019 at 11:54 am

      I’ve been tried to sole this problem for 12hours. Your comment about changing the display of screen helped me a lot!! Thanks!!

  12. Christina said on January 20, 2016 at 6:14 pm

    Thank you…don’t know why this happened but your instructions helped me fix it. Running Windows 10 and office pro 2007

  13. Oz said on July 22, 2016 at 3:20 pm

    Great tip! Thanks!

  14. Tracy said on September 1, 2016 at 4:48 pm

    Worked for me, too – thank you!!!

  15. shawn said on September 9, 2016 at 10:25 am

    It’s Worked for me, too
    thank you very much!

  16. Jari said on October 31, 2016 at 11:53 am

    I had a similar issue with Outlook 2013 on Windows 10 and this helped me to fix it. Thank you very much!

  17. Michel H said on November 30, 2016 at 11:08 pm

    Thank you so much. Solved!
    Considering you published this in 2012, incredible not been debugged by Microsoft.
    Thank you again. M

  18. Ziad Bitar said on January 9, 2017 at 2:00 am

    This problem was faced by only one user logging to TS 2008 r2 using outlook 2010.The issue was resolved.


  19. Anonymous said on February 15, 2017 at 5:24 pm

    Great tip. Thank you!!!! If it helps, I had to use the Control Key and the arrow keys at the same time to bring my window back into view. Worked like a charm.

  20. Rochelle said on March 6, 2017 at 11:59 am

    Thank you, this worked !!!!

  21. anom1234 said on May 20, 2018 at 11:20 pm

    Man, you are a fucking god. Thanks a lot, what an annoying bug!!

  22. JC said on October 12, 2020 at 2:14 pm

    Awesome, this post solved the issue. Many thanks!

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