Email headers are sections of an email message that contain metadata about the email, such as the sender, recipient, routing details, and authentication results. They are not usually visible in the main message body but are critical for troubleshooting and verifying email authenticity.
What Are Email Headers?
Email headers provide technical details that describe how an email was transmitted from the sender to the recipient.
While the message body contains the content that users see, headers hold important information for mail servers, internet service providers (ISPs), and security systems.
Key elements in an email header include:
- From: The email address of the sender.
- To: The recipient’s email address.
- Subject: The subject line of the email.
- Date: The time the email was sent.
- Message-ID: A unique identifier for the email.
- Received: Routing details that show each mail server the email passed through.
- Authentication results: Indicators for SPF (Sender Policy Framework), DKIM (DomainKeys Identified Mail), and DMARC (Domain-based Message Authentication, Reporting, and Conformance) checks.
These details are essential for verifying legitimacy, analyzing deliverability issues, and identifying spam or phishing attempts.
How Do Email Headers Work?
When an email is sent:
- The sending mail server generates an email header and includes metadata about the message.
- Each mail server that processes the email adds its own “Received” line to the header.
- Authentication protocols update the header with pass or fail results for SPF, DKIM, and DMARC.
- The recipient’s server uses this information to determine whether to deliver the email to the inbox, spam folder, or reject it.
Headers remain attached to the email and can be viewed through the email client’s “View Original” or “Show Headers” option.
Why Are Email Headers Important?
Email headers are critical because they:
- Verify sender authenticity: Help confirm whether the email passed authentication checks.
- Aid in troubleshooting: Diagnose deliverability issues and email routing problems.
- Detect spam and phishing: Reveal discrepancies in sending domains or forged details.
- Provide traceability: Show the path an email took through mail servers.
Without email headers, analyzing and resolving security or deliverability problems would be nearly impossible.
Common Use Cases
Email headers are widely used for:
- Email forensics: Investigating phishing or spoofing incidents.
- Deliverability optimization: Identifying routing delays or authentication failures.
- Compliance checks: Ensuring email campaigns meet authentication standards.
- Technical support: Resolving customer complaints about missing or delayed emails.
Example scenario: A marketer checks an email header to confirm why a campaign landed in the spam folder. The header shows that the email failed DMARC authentication due to misaligned domains.
FAQs About Email Headers
How can I view email headers?
Most email clients have an option like “Show Original” or “View Full Headers” in the message menu.
What’s the difference between headers and body in an email?
Headers contain metadata and routing information, while the body contains the visible content of the email.
Can email headers be forged?
Some parts, like the “From” field, can be spoofed, but full headers include server authentication lines that are harder to fake.
