by Arman Gungor
As forensic examiners, we often have to analyze emails in isolation without the benefit of server metadata, neighbor messages, or data from other sources such as workstations. When authenticating an email in isolation, every detail counts—we review a long list of data points such as formatting discrepancies within the message body, dates hidden in MIME boundary delimiters, and header fields.
One data point I often see being overlooked is the Content-Length header field. The value this field contains can be leveraged for a simple but powerful check to verify an email’s payload. In this post, I will discuss how we need to preserve emails to be able to utilize the Content-Length header field, how to utilize the data in this field, and a couple of use case scenarios. Let’s start by defining Content-Length.