1. Log into your Yahoo! mail with your username and password.
2. Click on Inbox or whichever folder you have stored your mail.
3. Open the mail.
4. 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
5. You should see similar headers like above
Or if you want to manually find the IP address, proceed to 6.
6. Look for Received: from followed by the IP address between square brackets [ ]. Here, it is 18.104.22.168.
That is be the IP address of the sender.
If there are many instances of Received: from with the IP address, select the IP address in the last pattern. If there are no instances of Received: from with the IP address, select the first IP address in X-Originating-IP.
7. Track the IP address of the sender