Good point! It used to be possible in outlook, but it looks like MS took that option away for years (WTF). Recently (within the last year) they said they brought it back. In Outlook 365 for Mac you should be able to right click on a message and select "View Source" to get the message with the full headers. That's the same way people did it in Outlook for Mac 2011
I agree, most people have no idea headers exist (beyond the short headers), but I expect lawyers and law enforcement to know better. Handling digital evidence is not new and at technology's timescale email is ancient.
