The user agent tells them the program or service that was used to send the email which can help evaluate the validity of the email. It should be noted however that the user agent is not always displayed.

It might raise suspicion for instance if a user has send emails from a specific program in the past while the latest email uses a different service or program.

Thunderbird users who want to add the user agent to the header information in the email software need to perform the following steps:

• Access the Options by clicking on Tools > Options in the header menu of Thunderbird.
• Switch to the Advanced tab and click on Config Editor, accept the warning message.
• Filter for the parameter mailnews.headers.showUserAgent
• Double-click the parameter to set it to true
• A restart might be required before the information are displayed.

The changes can be reverted by performing the same steps again. Do you have Thunderbird tips of your own? Let us hear them in the comments.

Most Thunderbird users probably do not need some of the information and options provided by default. This includes for example the information to whom the email was send or the action buttons like deleting emails which are also available on a right-click in the email itself.

That’s where the experimental add-on Compact Headers comes into play. The add-on is compatible with Thunderbird 3 only and can reduce the size of the email header to one row.

Thunderbird 3 Default Email Header:

Thunderbird 3 Compact Email Header:

The way the email header is displayed in compact form can be altered in the add-on’s options. It is possible to increase the size to two rows which can also hold some of the buttons that are provided in the standard Thunderbird header. Buttons can be individually selected in the options.

Compact Header for Mozilla Thunderbird 3 is an experimental add-on that is not automatically updating itself. The add-on comes with a “check for updates” button in the options. It is available at the Mozilla Thunderbird add-on repository at Mozilla.org.

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 a introduction “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.

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.