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:
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:
