Not totally sure what you're asking here...
To view the headers on gmail you should:
• Log in to your Gmail account.
• Open the message you want to view headers for.
• Click the Down arrow next to the Reply button, located at the top right of the message pane.
• Select Show Original.
It would contain the senders ip.
However, most email providers (including gmail, but I think yahoo doesn't) strip that data if the mail was sent from their servers to protect users privacy. In which case you'd only see the ip of the mail server, not the actual person.
So is this an email coming from gmail, going to gmail or both? whats the deal here O.O
<Yoda> if someone says something i don't like, i ban him, ban whoever defends him, and then ban the witnesses...