• Go to Mail -> Mail Display Settings
• Change the Message Headers section to Advanced
• On reading an email, all message headers will be visible

• On viewing an email -> More options
• Select Show original
• Full message headers will be displayed in a new window

• Mail Options -> General Preferences -> Show all headers on incoming messages
• On reading an email, all message headers will be visible

• Go to View -> Headers -> select "All"
• The headers are immediately displayed

• Right Click on the message -> Goto "Message Options" -> Headers

• Right click on the message -> Select Properties
• Choose the Details tab -> Message Source Button

When reading an email message, look at the toolbar just above the message itself. There should be a button labelled BLAH, BLAH, BLAH in black and white. Click on this and the full headers will appear.