How do I find out who sent the email?
Privacy laws strictly limit the information that online service providers like Yahoo may disclose about their users. However, an email message itself does contain some information relating to the sender's identity. In the headers of email messages, an Internet Protocol (IP) address that corresponds to the sender's Internet service provider (ISP) is included.
If you display full headers in your email application, you should find a line in the email message that contains an 8 to 12 digit number, separated by periods. It should look something like this:
Received: from [123.456.78.91\ by . . .
"123.456.78.91" represents the unique IP address of the sender's ISP. Once you have identified the IP address, you can run a search to determine which ISP provides this person with Internet access and possibly additional information as well.
There are many utilities available on the Web to run an IP search including: