The sender used a feature called "Blind Carbon Copy", abbreviated Bcc.

If you send an email to multiple addresses, the Bcc prevents all the addresses from showing up on each of the Recipients emails.

You can read more about this at: http://www.rrudder.com/safe/bcc.html


>I just received an unsollicited e-mail.
>
>In the "To:" portion there is a "Undisclosed-Recipient::"
>
>What is this?
>
>How does this work?