What Is the Header of an Email?
Definition
An email header is the behind-the-scenes metadata that comes with every email you send. It contains essential routing information that tells email servers where the message came from, where it's going, and how it got there.
It’s different from the “email header design,” which refers to your email layout’s top section. The email header is more technical and crucial for deliverability and spam prevention, and it has different components.
Components of an Email Header
A standard email header includes multiple fields, some visible to recipients and others used by email clients and spam filters for verification and tracking. Here are the key components of an email header:
- From: Shows the sender’s name and email address.
- To: Displays the recipient’s email address.
- Subject: The subject line that appears in the recipient’s inbox.
- Date: Timestamp of when the email was sent.
- Message-ID: A unique identifier assigned to each email.
- Return-Path: The address where bounce-backs are sent.
- Received: Shows the servers that processed the email, listed in reverse order.
- DKIM/SPF/DMARC: Authentication protocols used to verify sender identity and fight spoofing.
- MIME-Version & Content-Type: Define the format of the message and how it should be rendered.
Optional fields may also appear depending on the email service or mailing platform used.
Example
Let’s say a marketing team notices that their open rates have plummeted. By checking the email header, they spot a failed DKIM signature, which indicates that their messages aren’t passing authentication checks. Fixing the DKIM record improves inbox placement, which brings their engagement metrics back on track.
Importance of Email Headers
Email headers are vital beyond just routing. They’re a key tool in diagnosing delivery issues, checking authenticity, and improving overall inbox placement. Here’s how they support marketers and business users:
- Verify email authentication: Tools like SPF, DKIM, and DMARC records in the header help prove your email is legit. This builds trust with receiving servers and reduces your risk of getting flagged as spam.
- Troubleshoot deliverability problems: If your email goes missing or ends up in spam, a quick look at the header can help trace whether it was delayed, blocked, or bounced—and help you identify the reason for it.
- Protect your domain reputation: Monitoring email headers can alert you if someone’s trying to spoof your domain, which can tank your sender reputation if not caught early.
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