I am going to introduce you a simple trick to find the IP
address of anyone who has sent you an email in Yahoo mail service without need
of any special software.
First of all go to your Yahoo mail and open the mail
you want to find the IP address of its sender. If you use Yahoo Mail Classic,
from the bottom of the page click on the Full Header and if you’re using the
new Yahoo Mail service, from the top menu click on Action, then Full Header. Now
you can see the sender’s IP address in front of X-Originating-IP.