When you receive an email message, the message also includes a set of information called the "headers", which tells you precisely how the message found its way from the sender's mail server to your inbox. Chances are, the mail will have travelled through more than one additional server, and those headers will give you the full story.

Being able to examine an email's headers is useful when you're trying to troubleshoot problems, such as finding the origin of an annoying spam message or if you want to know why your email is taking so long to arrive in your inbox. Where is the delay occurring? Is it with your email provider, or further up the chain?

Unfortunately, email headers, while easy to obtain, are difficult to understand. They're not in a user-friendly format. Thankfully, there are a number of web-based systems into which you can paste a set of headers and receive back the data in a much more usable form. My favourite is MX Toolbox, which you'll find at http://mxtoolbox.com/EmailHeaders.aspx if you want to try it. Just paste the header data into the form on the page, press the button, and get the results pretty much instantly.

This just leaves the issue of how to find the headers attached to a message. This, sadly, varies according to the email provider or program that you're using. In the case of Gmail, for example, just open a message and then, in the drop-down menu on the right hand side, choose Show Original.