FINDING IP ADDRESS OF THE SENDER IN YAHOO! MAIL

Log into your Yahoo! mail with your username and password.

Click on Inbox or whichever folder you have stored your mail.

Open the mail.

If you do not see the headers above the mail message, your headers are not displayed . To display the headers,
Click on Options on the top-right corner

In the Mail Options page, click on General Preferences

Scroll down to Messages where you have the Headers option

Make sure that Show all headers on incoming messages is selected
Click on the Save button

Go back to the mails and open that mail.

You should see similar headers like this:
Yahoo! headers : Mastitrain.

Look for Received: from followed by the IP address between square brackets [ ]. Here, it is 202.65.138.109.

That is be the IP address of the sender!