Thunderbird client:
You can send yourself a copy of it and then view the raw message using menu option View → View Source
Outlook:
Open the message you want to see the source code of in Outlook.
(2010) right click on the message and select "View source"
or
(pre 2010) From the menu bar, click Other Actions then View Source from the drop down.
(2010) In the "message" tab, look in the "move" section and select "Actions" -> "Other actions" -> "view Source"
Gmail:
Click on the down arrow next to Reply or More Options -> Show original
OK, there it is:
From Daniel Buchmann Tue Oct 27 13:00:02 2015
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Message-ID: <54bd96b95f6a7006752546f8ee26f123@swift.generated>
Date: Tue, 27 Oct 2015 13:00:02 +0000
From: Daniel Buchmann <daniel.buchmann@bc.adm.br>
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