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One Step Ahead
February 10, 2009, Volume 55, No. 21

One Step Ahead

Another tip in a series provided by the Offices of Information Systems & Computing and Audit, Compliance & Privacy.

E-mail Headers: Getting the Full Story

Whether it’s common spam or messages that are actually threatening or disturbing, Penn Information Security is often asked about how to identify the sources and senders of troublesome e-mail. Because e-mail is so easily forged, it’s usually the case that conclusive identification of who and where a “bogus” message came from is not possible. There are instances, though, where the information contained in the message headers can indicate or strongly suggest the source. Similar to the information found on the envelope in which a postal letter is sent (address, return address, postmark), e-mail message headers are sort of an “electronic envelope” that may contain literally dozens of bits of data about how the message was sent.

Most ordinary e-mail users are familiar with only a handful of these headers —“To:,” “From:,” “Cc:,” “Subject:,” “Reply-To:”—because most e-mail programs consider these the only ones the user is really interested in and “helpfully” hides the rest from view under normal circumstances. With few exceptions, though, modern e-mail programs also provide an option to display the “full headers” for inspection. Like the “From:” header, many of these hidden headers can be forged or manipulated, but others are very difficult to fake. For example, each message will have a series of “Received:” headers which detail the mail servers through which the message travelled, and these are extremely difficult to forge. So, if you receive what looks like a message “From: upenn team,” but the headers indicate the sending server is from a “.ru” (Russia) or “.cn” (China) domain, you can be pretty confident it’s not really from a Penn source.

If you’re using Outlook, here’s how to display the full message headers:

1. Open the message in its own window by double-clicking the message.

2. Select View-> Options.

3. In the Internet Headers window, you’ll see the full headers.

For how to do this with other e-mail programs, the spam reporting service SpamCop has a very useful page at www.spamcop.net/fom-serve/cache/19.html. A final note: if you are ever asked to provide a suspicious or troubling e-mail message with full headers to authorities for investigation, simply using the “Forward” button will not suffice, because your server will simply replace the original headers with its own. In this instance, display the full headers along with the message body, cut-and-paste all of it into a new message and send that.


To receive weekly OneStepAhead  tips via email, send email to listserv@lists.upenn.edu with the following text in the body of the message:  sub one-step-ahead <your name>.

For additional tips, see the One Step Ahead link on the Information Security website: www.upenn.edu/computing/security/.

Almanac - February 10, 2009, Volume 55, No. 21