Email Header

An email header is the set of fields before the message body: From, To, Subject, Date, Message-ID, and technical lines added by each server. Most clients hide most of it, but a "show original" or "view source" option reveals the full text.

Why it matters

Headers are how you diagnose delays, spam placement and authentication. Each server that handles a message prepends a Received line, so reading them from bottom to top shows the route and timestamps; a large gap between two lines shows where the delay happened. The Authentication-Results header records the receiver's SPF, DKIM और DMARC verdicts. Anything below the receiving server's own lines can be forged by a sender, so trust only lines added by servers you control.

Example

Authentication-Results: mx.example.net;
  spf=pass smtp.mailfrom=news@sender.test;
  dkim=pass header.d=sender.test;
  dmarc=pass header.from=sender.test
Received: from mail.sender.test (203.0.113.25) by mx.example.net; Mon, 5 Oct 2026 09:14:02 +0000

Common mistakes

• Believing the top Received line proves where mail started; it only shows the last hop.
• Trusting forged lower Received lines.
• Copying headers into a public ticket without removing private addresses.

Related

• From Header
• Envelope Sender
• SPF
• DKIM
• टूल: Email deliverability test

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