An email header is the section at the top of every email that carries metadata about the message — who sent it, who it's to, the subject, the date, and routing and authentication details. Most of it is hidden by default.
What's in an Email Header
The visible header shows From, To, Subject, and Date. Behind it sits a larger technical header with fields like Received (the servers the message passed through), Message-ID, Reply-To, and authentication results for SPF, DKIM, and DMARC. These fields tell receiving servers where a message came from and whether it can be trusted.
Why Email Headers Matter
Headers drive deliverability and security. Authentication fields help inboxes decide whether to deliver, filter, or reject a message, which directly affects whether you land in the inbox or spam. Headers are also used to trace a message's path when troubleshooting, and to detect spoofing or phishing. For marketers, a clean From name and subject — the visible header — shapes whether recipients open the email at all.
Email Header and Topol
Strong subject lines and sender names work hand in hand with well-designed content. Create compelling, professional emails with Topol, start free at Topol signup, or browse more terms in the Topol glossary.