How to View All Email Headers in Mac OS X Mail

The Mail app in macOS and OS X can show you all an email's header lines, which contain possibly important and usually hidden information. You may never need to look at the header lines, but if you ever have problems with your email, a technician may ask you for information contained in the normally hidden header.

Email headers offer access to many of an email's details, such as its path, email program, and spam filtering information. In Mail, you don't have to open the full message source to access all the header lines for a message.

You can get a display of all the usually hidden header lines right in the message itself. Once there, you can look for X-Unsubscribe information, for example, that lets 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 to your Mail inbox.

View All Email Headers in Apple Mail

To have the Mac Mail app display all an email message's header lines for a specific email:

1. Open the message in the macOS or OS X Mail reading pane or in its own window.

2. Select View in the menu bar and choose Message > All Headers from the drop-down menu.

   You can also use the keyboard shortcut Command+Shift+H to reveal (or hide) the expanded email headers.

3. Look at the top of the email for the expanded headers. They may be only a few lines, but most emails have lengthy headers. You may need to scroll down to see all the headers, and most of them won't make a lot of sense to you, but in the right hands, they are valuable.

Hide Full Header Display in Mail

To revert to the message in the regular display, select View > Message > All Headers again from the menu bar or use the Command+Shift+H keyboard shortcut.

Are Headers Displayed With Their Original Layout?

Note that macOS Mail and OS X Mail show some header lines out of their original order and with formatting when you turn on full header view, including:

• The From header appears as the message's sender.
• The To header appears as the To line with formatted email address or addresses.
• The Cc header appears as the Cc line, either with a formatted email address or an expandable link to additional email addresses.
• The Subject line appears in formatted text with the Re: prefix.

View Raw Source Headers

If you prefer to access all the header lines in their original order and without any formatting—just as they arrived in your email account—you open the raw source code:

1. With the email open in macOS or OS X Mail, select View on the Mail menu bar and choose Message > Raw Source in the drop-down menu.​

   You can also use the keyboard shortcut Command+Alt+U to reveal the raw source headers.

2. View the email's raw source in a separate window titled Source of [Email Subject]. You may have to scroll down to see all the content.