*trick to find out IP address in gmail from unknown sender:
Finding IP address in Gmail

1. Log into your Gmail account with your username and password.
2. Open the mail.
3. To display the headers,
* Click on More options corresponding to that thread. You should get a bunch of links.
* Click on Show original
4. You should get headers like this:
Gmail headers : name
Look for Received: from followed by a few hostnames and an IP address between square brackets. In this case, it is

65.119.112.245.
That is be the IP address of the sender!
5. Track the IP address of the sender