Finding IP address from eMail

Finding out someone's IP address can be useful in number of ways. Sometimes I check if my friend has a BSNL net (using his IP) and make them download things for me.
How do you find out IP address?
One of the easiest ways is to check the email header.
If you have received an email, the IP address of the computer is embedded in the email header.

In Yahoo mail, click on the "Full Header" at the bottom of the message. In Yahoo Mail Beta, click on the link as shown in the figure and select "Full Header".
Similarly on GMail, beside the reply on the right side of the message, there is an arrow as shown in the picture. Then select "Show Original"

This will give you an output that will be similar to the following

Now you can either simply copy the header and goto http://whatismyipaddress.com/staticpages/index.php/trace-email-source-IP-address and paste the header there to get the IP address. Or you can see closely and see in the above figure in the "Received:" there is an IP address 202.62.89.12, this is the required IP address. Then use this IP address to find more information about it. The main information that you can get are: ISP, location.
You can use http://www.whatismyipaddress.com http://www.whois.net http://www.geoiptool.com to gather more information about that IP.
Sometimes I ask people to mail me, when they do, I tell them "you have .... net na, I know".