When addressing an e-mail there are three address boxes. The first is To: the second Cc: which stands for carbon copy, and the third is BCc: which stands for blind carbon copy. Any e-mail address in the BCc field will receive the e-mail, but their e-mail address wont appear on the actual e-mail. This is so you can copy someone in on the e-mail without the recipient being aware. Unfortunately, it is often used by people sending spam.