What Are Email Headers?
Email headers are metadata fields at the top of every email message that record information about the sender, recipient, routing path, timestamps, and authentication results. They are essential for diagnosing delivery problems and detecting email spoofing.
How Email Headers Work
Each email consists of headers and a body, separated by a blank line. Headers are key-value pairs like From: sender@example.com. As the email passes through each mail server, new Received headers are added at the top, creating a traceable routing chain from origin to destination.
Key Email Headers
From — the sender's display address. Return-Path — the envelope sender (bounce address). Received — added by each server, showing the routing path. DKIM-Signature — the DKIM cryptographic signature. Authentication-Results — SPF, DKIM, and DMARC verification results added by the receiving server. Message-ID — a unique identifier for the message.
Using Headers for Troubleshooting
Email headers reveal where delivery delays occur (by comparing timestamps in Received headers), whether authentication passed or failed (Authentication-Results), which server rejected the message, and whether the From address matches the actual sender. This information is critical for debugging bounces, spam filtering issues, and spoofing attacks.
Frequently Asked Questions
What are the most important email headers?
From, To, Subject, Date, Received (routing), Message-ID, DKIM-Signature, Authentication-Results, and Return-Path are the most important for debugging and security analysis.
How do I view email headers?
In Gmail, click the three-dot menu and select "Show original." In Outlook, open the email properties. In Apple Mail, go to View > Message > All Headers. You can then paste the raw headers into our analyzer for easy reading.
Can email headers be faked?
The From, Reply-To, and Subject headers can be forged by the sender. Received headers added by intermediate servers are harder to fake. Authentication-Results added by the receiving server are trustworthy because they are independently verified.