How to View All Email Headers in Mac OS X Mail

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Peek at email headers in macOS Mail from behind, above, or anywhere else. StockUnlimited

macOS Mail and OS X Mail can show you all an email's header lines—which contain possibly important and usually hidden information.

You Want Them All?

Want to see it all? Want to see just enough?

Email headers offer access to many an email's detail, such as its path, email program or spam filtering information. In OS X Mail, you do not have to open the full message source to access all header lines for a message.

You can get a display of all the usually hidden header lines right in the message itself, and look for X-Unsubscribe information, for example, that would let you know how to sign off an email list or examine Received: lines to see which path an email took to get from the sender into your macOS Mail inbox.

View All Email Headers in Mac OS X Mail

To have OS X Mail display all an email message's header lines:

  1. Open the message in the macOS or OS X Mail reading pane.
    • You can also open the email in its own window.
  2. Select View | Message | All Headers from the menu.
    • You can also press Command-Shift-H (think "h-eaders", of course).

Hide Full Header Display in OS X Mail

To revert to the message in regular display:

  • Select View | Message | All Headers again from the menu or press Command-Shift-H.

Are Headers Displayed with Their Original Layout?

Note that macOS Mail and OS X Mail will show some header lines out of their original order and with formatting when you turn on full header view as above.

Specifically,

  • the From: header will appear as the message's sender,
  • the To: header will appear as the To: line (with formatted email address or addresses),
  • the Cc: header will appear as the Cc: line (with formatted email address or addresses),
  • the Reply-To: header will appear (again, with formatted email address or addresses) and
  • the Subject: line will appear at the header lines' very bottom without the Subject: prefix.

View All Headers in Their Original Order and Layout

To get access to all the header lines in their originally order and formatting—as the arrived in your email account:

  1. Select View | Message | Raw Source from the menu in macOS Mail or OS X Mail.
    • You can also press Command-Alt-U.
  2. Find the header lines at the very top of the Source of [Email Subject] window.
    • The first line of the email body is the first line following an empty line from the top.
    • The last line before the first empty line from the top is the last line of the email headers.

(Updated August 2016, tested with OS X Mail 6 and 9)