Understanding Email Headers: A Technical Deep Dive
A comprehensive look at email headers and what they reveal about message routing and security.
Email headers contain valuable information about the journey an email takes from sender to recipient. Understanding these headers can help you identify spam, verify authenticity, and troubleshoot delivery issues.
What Are Email Headers?
Email headers are metadata attached to every email message. They contain information about:
- The sender and recipient
- The email servers that handled the message
- Authentication results
- Timestamps at each hop
Key Header Fields
From and To
These fields show the apparent sender and recipient. However, they can be easily spoofed, so they shouldn't be trusted blindly.
Received Headers
Each server that handles an email adds a "Received" header. Reading these from bottom to top shows the email's journey.
Authentication Headers
Modern email systems include authentication headers like:
- SPF (Sender Policy Framework): Verifies the sending server is authorized
- DKIM (DomainKeys Identified Mail): Provides a digital signature
- DMARC (Domain-based Message Authentication): Combines SPF and DKIM policies
Reading Headers for Security
Identifying Spoofed Emails
Compare the "From" field with the authentication results. If DKIM or SPF fails, the email may be spoofed.
Tracing Email Origins
Look at the bottommost "Received" header to find the original sending server's IP address.
Conclusion
Email headers are a powerful tool for understanding email security and routing. While they may seem complex at first, learning to read them can help you identify potential threats and verify email authenticity.