How to Show Full Email Headers in Mail for Mac OS X

Some users may wish to see the complete email header attached to email messages in the Mail app for Mac OS X. These long headers can reveal many details about the sender of an email message, including the origin mail servers and IP addresses, original arrival time, email alias details, and much more, making them a potentially valuable resource for some situations, particularly for users wishing to authenticate the validity of an email or mail message. Additionally, email header information can be very helpful for troubleshooting complicated email server issues.

The Mail app in Mac OS X makes it easy to display the complete email headers for mail messages, we’ll show you how to show the full header, return to the default header, and a rapid access keystroke to toggle the display of full email headers off and on quickly as needed.

Note this is generally best reserved for advanced users who understand how to interpret the email header data, as the average user will likely just find the email header to be unnecessary gibberish that complicates an email message.

How to Show Complete Email Headers in Mail for Mac OS X

This applies to all versions of Mail in all releases of Mac OS X system software:

1. Open Mail app if you haven’t done so already and select or open any message in the inbox
2. Pull down the “View” menu and go to “Message”, then select “All Headers”



3. Review the email header details at the top of the email message

You’ll find that email headers are generally quite lengthy as they are full of various details about the mail servers involved, content types, IP addresses, and much more.

Again, the complete header detail data is not really meant to be interpreted by an average email user, this is generally best for advanced users who have some experience accurately interpreting and reading the header details, which often look like a bunch of hexadecimal nonsense, dates and times, server names, and IP addresses. But, as a general rule, users can determine if a message is authentic by reviewing the header for an email message and checking to see if the header information corresponds properly with who the sender claims to be. For example, if an email claims to be from Microsoft, all relevant header information for mail servers for that message should be from “microsoft.com” or a relevant subdomain. If the sender information or claim within an email does not match up with the email header information, you may have reasonable suspicion that the sender is not who they say they are, but again, this is a generalization and that is not always true.

Hiding Full Email Headers in Mail for Mac (the Default Header Display)

Had enough viewing the complete header and want to return to the default header view in Mail for Mac? That is just as easy:

1. From the Mail app, select any email message as before
2. Return to the “View” menu and choose “Message” and select “Default Headers”

Toggling Full / Short Email Headers with a Keystroke

Mac Mail users can also toggle the email header from the full complete header to the default short header, and vice versa, using Command + Shift + H from any email message.

Most Mac users will find that having the full headers shown for email message is quite unnecessary, but it can be helpful to toggle the display of the complete header on temporarily sometimes to validate an email, or to help rule out problems with email servers, and then toggle the display back off to return to the regular email header view again.