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Unsolicited Outreach

Header decoder.

Paste an email's headers and get the story in plain English: who really sent it, what your mail server checked, and the path it took. Everything happens in your browser. The headers never leave this page.

Paste everything from the top of the message source down to the first blank line. Including the body is fine; it's ignored. Nothing here is sent anywhere.

How this works

  • The decoder is a script that runs on this page. There is no request to our server when you click Decode, and nothing is saved. You can check that in your browser's network panel.
  • It reads the Authentication-Results header your own mail server added, so the verdict is what your server decided, not a new check. If that header is missing, it says so.
  • Received headers are listed oldest first, so the first row is where the message entered the mail system.
  • Every statement is a fact read from a header. Whether a message is wanted is your call; the decoder shows you what it did.

Why a message can pass every check and still be unwanted: read the explanation.