Find out from where an email has been sent

Hi all,

I'd like to find out from where an email has been sent.

I already know I have to to find the "Received From" that’s farthest down in the complete headers to get the private and the public IP addresses.

But I'm a little bit confused when the private IP is [127.0.0.1].
Could we say it means that the mail has been sent from the same LAN than the mail server (public IP adress) ? Or that the mail is read on the same PC that has sent the email ?...

Thanks a lot in advance for your answers !