When you receive an email that email contains an email address that supposedly is the address that was used to send the email. It is possible, particularly with spam emails that this return address has been faked and is not the real address from which the email was sent. In order to take any action against the ISPs who are allowing this spam to be sent from their servers we need to determine where the email has really come from. This can be easily done by examining the email header information which contains information about every mail server that the email has passed through from the originating server through to your mail server (the destination).
To access this information with Outlook Express you first need to select the email whose headers you want to examine. You then need to go into Properties. You can access this by pressing Alt and Enter together or by selecting the option from the File menu or from the context menu by right clicking on the mail entry.
In the Properties select the Details tab. This will display the headers for the selected email. The top line (Return Path) gives the return email address the same as you see when you view the email normally but on the lines below that it shows one or more Received from lines that contain information about each of the mail servers that the email has passed through on its way to you starting with the most recent one (which should be your mail server) and followed by all of the other mail servers that the email has passed through on its way to you. The last server listed is the mail server that was used to enter the email into the internet mail system in the first place and so is the one that you would need to complain to your ISP about if you are receiving lots of unwanted spam from the same originating server.
Note that selecting the Message Source button at the bottom of the page will display the entire source of the email in raw form enabling you to see everything contained within the email not just the information translated and displayed by your email program. This is particularly useful for seeing the source of emails in html format
This article written by Stephen Chapman, Felgall Pty Ltd.