Being able to view e-mail header information can be useful, but sometimes OS X Mail's settings may prevent you from easily seeing headers.
Topher KesslerMacFixIt Editor
Topher, an avid Mac user for the past 15 years, has been a contributing author to MacFixIt since the spring of 2008. One of his passions is troubleshooting Mac problems and making the best use of Macs and Apple hardware at home and in the workplace.
When you receive an e-mail in Apple's Mail client, you will by default see a few header details such as who the message was from, the date, subject, and who the message was sent to.
While this is the default view for e-mail messages, there are some settings that can result in the header information being changed or hidden, which can cause a bit of frustration for people who wish to see additional information.
Recently MacFixIt reader Don wrote in with such a problem where his desired header settings were not working properly:
In [Mail's Viewing preferences] I've selected Show Header Detail: All; however, only the To address shows. This is inconvenient when replying-all. Clicking on Details in the message shows the entire mail header details--not what I want to see.
If you are having similar problems with Mail's header information views, you can try the following options:
Toggle header view information
By default Mail shows only a basic header set, but you can choose to show more header options by pressing Shift-Command-H or by selecting "Show all headers" from the View > Message menu. First try toggling this view to see if Mail will show the header information you want.
Clicking this link will show or hide detailed header information for the message.Screenshot by Topher Kessler
Click the Details link
In addition to selecting the headers, at the top of each e-mail message you should see a small blue text link that either says "Details" or "Hide." If you click this, Mail will toggle between showing the header details and only displaying a simple header, so try toggling this option to see if it shows the information you want.
Set the information to display in the Details link
If Mail is set to show header details instead of the basic header information, but it's also set to show only a couple of header items, the result will be a minimal header. This was the problem in Don's case: Mail was set to only show a few options when the details were shown. To overcome this, Don had to go back to the Mail preferences and change the header details setting.
To add custom headers in the details list, click the plus sign and then type them exactly the way they are displayed in the message's raw source.Screenshot by Topher Kessler
To alter the headers that Mail includes, you can go to the Viewing section of the Mail preferences, choose the Custom setting, and then add or remove any fields of the e-mail header that you wish to see. Unfortunately you need to enter the field names manually, and many times e-mail services will append their own header details to a message, especially for handling spam or other security features. Therefore if you are not sure what the header titles are then you will need look them up in the raw source code for any particular message.
To do this, select a message in your inbox and then press Option-Command-U or choose "Raw Source" from the View > Message menu. In the resulting window you will see all the message details in plain text. Header fields will be the text before colon characters with dashes in them in place of spaces, and may include items like "Delivered-to:" or "Return-Path:", or custom items like "X-Virus-Scanned:" for antivirus information.
When entering these details in the custom headers list, be sure to enter them as is (including the dashes), after which be sure that Custom is selected in the preferences and that the Details link is clicked in your e-mail messages.
