Gmail Sender IP Extraction

I have a specific Gmail message and I need the sender’s real IP address pulled from it so I can confirm who actually sent it and then reach out to that person directly. You may work with the raw headers if you like, but the only piece of information I want back is the originating IP itself—no extra header analysis, no personal data beyond that.

Here’s what I will supply: a copy of the email (either the full header text or the .eml file, whichever you prefer).
What I expect in return:
• The sender’s IP address, clearly shown.
• A brief note (a line or two) describing exactly where in the header you located it, so I can verify your findings later.

Any widely-accepted technique is fine—manual header parsing, a trusted header-analysis tool, or a short script—so long as the result is accurate. If the message was sent through a relay that masks the original IP, please state that clearly instead of guessing.

Speed is important; once you have the email, I’d like the answer within a day if possible.