Understanding Email Headers

Martin Brinkmann
Jun 15, 2006
Updated • Mar 14, 2014
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Everyone knows how to send and receive emails but only a few understand the concept behind the process.

What is actually happening when you click on the send button?

Emails are not sent directly from your machine to the recipient's computer. Mail servers that are setup by your ISP or the email provider you are using for instance process incoming emails and transfer them to their destination.

The information are stored in email headers so that mail servers know where to transfer the mails to. This is very similar to how the local post office handles your postcards. They look on the cover to find out where the letter needs to be sent to.

Why postcards? Because all email contents are readable unless you use some form of encryption. If you do not, and the majority of Internet users does not, your emails are readable by every server and everyone listening in as they pass through on their way to the destination.

Email headers can help you a lot, especially when it comes to spam and malicious emails that you may receive in your email inbox. The concept is similar to regular letters. Just like it is possible to write any sender address and name on envelopes or postcards, it is possible to do the same for email recipient addresses.

The article "reading email headers - all about email headers" gives you an in depth overview about email headers.

Everything is explained with examples which makes it easy to follow through, even for people who lack the tech background.  It begins with an introduction that explains "where mail comes from" and details "mail protocols" thereafter. The final part consists of a list of common mail headers which is great if you want to understand a certain part of the header.

email header part

Update: The guide is divided into four chapters. Displaying email headers explains how you display email headers in popular email clients such as Outlook, Netscape or Eudora. Please note that the article has been written in a time where popular clients like Thunderbird have not been created yet.

Received headers detail the emails origin and the route it took to get to you. These information are displayed in reverse order which means that the last received header in the email is in fact the first that received the email, and the first in the listing is usually the mail server of the email provider.

The last received header details what you can find out about the first server that processed the email. This can be helpful to identify the origin of the email which in turn can be used to report an email as spam or malicious.

Other headers finally lists other common email headers that you may come upon in emails.

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Comments

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

    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
      Reply

      I think its thunderbird

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

      It is Mozilla Thunderbird.

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

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

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

    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
      Reply

      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
      Reply

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

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

      Fantastic. Thank you. Size did the trick.

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

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

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

    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
    Reply

    You are a god – thank you!

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

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

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

    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
    Reply

    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
    Reply

    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
    Reply

    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
      Reply

      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
    Reply

    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
    Reply

    Great tip! Thanks!

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

    Worked for me, too – thank you!!!

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

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

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

    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
    Reply

    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
    Reply

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

    Thanks.

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

    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
    Reply

    Thank you, this worked !!!!

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

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

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

    Awesome, this post solved the issue. Many thanks!

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