Thunderbird is a great open source email client. I have used it on and off over the years. It works great and is updated often.
How to View Email Headers in Thunderbird
1. Open Thunderbird
2. Double-click to open the email message
3. From the menu bar select View > Headers then choose All
4. The headers should be immediately displayed
Matt is a Systems Development Director for a multinational franchise. Matt has lived and worked in Hawaii, Chicago, South Florida and currently resides outside of Atlanta. He enjoys his hobbies including Technology, Gadgets/EDC, Fountain Pens, Wetshaving, Clocks, Antiques & Coffee. He even roasts his own coffee weekly.