Email headers are the metadata that accompany an email and provide vital information about its origin, path, and delivery.
By default, email headers are not visible to the recipient when viewing an email through a typical webmail interface. This is primarily to simplify the user experience and avoid overwhelming users with technical information.
However, Digital forensics experts rely on these headers to investigate cybercrimes, track email sources, analyze communication patterns, and verify the integrity of email messages.
Email header information
The email header contains a range of information, below is a list of the data it typically stores:
Return-Path: Specifies the email address to which bounced or undeliverable messages should be returned.
Received: A chain of headers indicating the servers or systems the email passed through during transmission, which includes timestamps, IP addresses, and hostnames.
Delivered-To: Specifies the email address or mailbox where the message was delivered.
Received-SPF: Indicates the result of the Sender Policy Framework (SPF) check, which verifies if the email’s origin server is authorized to send emails for the claimed domain.
Authentication-Results: Provides the results of various email authentication methods, such as SPF, DKIM, and DMARC.
DKIM-Signature: Contains the cryptographic signature generated by the sending domain to verify the integrity and authenticity of the email.
DomainKey-Signature: A deprecated method similar to DKIM for verifying the authenticity of the email.
From: Specifies the email address and, optionally, the name of the sender.
Reply-To: Indicates the email address to which replies should be sent, which may differ from the sender’s address.
To: Primary recipient’s email address.
Cc: Lists the email addresses of additional recipients who receive a copy of the email.
Bcc: Similar to Cc, but the email addresses of Bcc recipients are hidden from other recipients.
Subject: The subject line or title of the email.
Date: Indicates the date and time when the email was sent.
Message-ID: A unique identifier assigned by the email server to the message.
In-Reply-To: Specifies the message ID of the email to which the current email is a reply.
References: Contains a list of message IDs referring to previous related emails in a conversation.
MIME-Version: Specifies the version of the Multipurpose Internet Mail Extensions (MIME) standard used for encoding the email.
Content-Type: Describes the type of content within the email, such as plain text or HTML.
Content-Transfer-Encoding: Indicates the encoding method used for transferring the content.
X-Priority: Specifies the priority level of the email.
Importance: Indicates the importance level of the email, such as low, normal, or high.
User-Agent: Identifies the email client or software used to send the email.
X-Mailer: Specifies the software or program used to send the email.
X-Originating-IP: Indicates the IP address of the device or server from which the email originated.
X-Sender: Specifies the email address of the sender.
X-Original-Sender: Indicates the original email address of the sender, which may be different from the From address.
X-AntiAbuse: Contains information related to anti-abuse measures taken by the email system.
X-AntiAbuse-Source: Indicates the source of potential abuse, such as the originating IP address.
X-AntiAbuse-UserAgent: Specifies the user agent or software used by the sender to compose the email.
Digital Forensic Focus
Email headers are of great importance in digital forensics investigations. Email headers serve as a valuable source of information that can help in verifying the authenticity of emails, tracking the flow of communication, and attributing email messages to specific individuals or entities. Below are a couple of key areas to focus on when conducting investigations involving email headers:
Email Source Identification: Email headers provide information about the source of an email, including the IP addresses and domains of the sending and receiving mail servers. This information can help trace the origin of an email and identify potential sources of malicious activity.
Timestamp Analysis: Email headers include timestamps that indicate when the email was sent, received, and delivered. These timestamps can be crucial in establishing timelines, determining the sequence of events, and correlating email communications with other digital evidence.
Email Routing Information: Email headers contain details about the mail servers involved in the delivery of an email. Forensic investigators can analyze this routing information to understand the path the email took and identify any other involved parties. This can be useful in tracing the route of malicious emails or identifying potential points of compromise.
Message Integrity Verification: Email headers often include cryptographic signatures, such as DKIM (DomainKeys Identified Mail) and SPF (Sender Policy Framework). These signatures can be used to verify the authenticity and integrity of the email, ensuring that it has not been tampered with during transit.
Email Metadata Analysis: Email headers provide metadata about the email, such as the email addresses of the sender and recipient(s), subject lines, and message identifiers. This metadata can be analyzed to establish communication patterns, identify relationships between individuals, and reconstruct email conversations or threads.
Tracking Email Forwarding and Redirection: Email headers may contain information about email forwarding, redirection, or replies. Forensic investigators can examine these headers to understand the flow of information, track the path of email messages, and identify any alterations or manipulations of the email chain.
Header Manipulation Detection: Email headers can be analyzed to detect any attempts at header manipulation. This can help identify spoofed emails, phishing attempts, or email fraud schemes.
Analysis of Error Messages and Bouncebacks: Email headers contain information about delivery status notifications, bounce messages, and any encountered errors during the delivery process. This information can be used to gather evidence of email delivery issues, identify potential tampering or interference, or trace the existence of intermediary mail servers.
Email Header Script
I scripted a code that presents an interface that allows users to browse and select an email file, extract its header information, and display the extracted contents in a user-friendly manner.
To access the script, you can download it from the following GitHub repository: Email Header.py
Below are the instructions to execute the program:
1. Execute the script.
2. The GUI window will appear, and you can proceed by clicking the “Browse” button.
3. Choose an email file in .eml format using the file dialog that opens.
4. The script will extract the header information from the selected email file.
5. A new GUI window will open, displaying the extracted header information.
Note: This script assumes that the email file is in UTF-8 encoding. If your email files are encoded differently, you may need to adjust the encoding accordingly in the extract_header_info function.
To run this script, make sure you have the following prerequisites:
-
- Python 3 installed, which should include the tkinter module by default for GUI functionality.
- Ensure that the PIL (Python Imaging Library) module is installed. If it’s not already installed, you can install it by running the following command: `pip3 install pillow`.
Email Parsing Details:
The extract_header_info() function takes the filename as an argument. It opens the selected email file, reads its contents, and uses email.message_from_file() to parse the email message.
The function then creates an empty dictionary called header_info to store the header information. It iterates over the headers in the email message (msg._headers) and extracts the name and value of each header.
The function attempts to decode the header value using decode_header(). If the value is encoded, it decodes it using the appropriate encoding (typically UTF-8). The decoded value is then added to the header_info dictionary with the header name as the key.
Conclusion
In conclusion, email headers play a crucial role in digital forensics investigations. They provide valuable information for tracing the origin, path, and authenticity of an email. Email headers allow forensic analysts to identify the sender, recipient, and intermediate servers involved in the transmission, helping to establish timelines, track the email’s route, and verify its integrity. Additionally, email headers can reveal crucial details such as IP addresses, cryptographic signatures, and authentication results, which are vital in investigating cybercrimes, phishing attempts, and other fraudulent activities. Therefore, the analysis of email headers is a fundamental component of digital forensics, enabling investigators to unravel the evidence and uncover insights essential for resolving cases and ensuring the integrity of electronic communications.