Yahoo Mail services allows users to see the full header details of an email. If you have suspicion on a particular email and want to see more information about the email sender then you can use this feature.
To see the full header details of the email, Login in to your yahoo mail account and select the email for which more information is required. From the menu option, click the down arrow available below the Actions menu.
From the list of available action menus, select View Full Header
The following Full Message Headers window will be displayed with more information about the email sender.