""From" addresses can be forged .... incredibly easily, and with no special software, coding or "hacking" required."
"In order to correctly evaluate the authenticity of an email, the ONLY way to look at the email source and go through the full raw email headers."
Correct. If it is spam or malware there will be a clue in there somewhere.
Mac
And I find Mailwasher -
MailWasher Pro - Superior anti spam filter software | Firetrust - invaluable for deleting crap on the mailserver before it hits your computer.
(Mix - please don't let us start that argument again - please)