In Outlook Express, there is an option for CCing (carbon copying)
and BCCing (blind carbon copying) intended recipients. Just click the TO button next
to the address field and a new window will pop up exposing the BCC box at the bottom.
Select your desired address and click the BCC button, then click OK.
When a sender enters addresses only into the BCC field, and sends
with an empty TO field, those messages are received as "undisclosed
recipient."
The use of the BCC field is actually a very practical one. How
many times have your received forwards only to find that your email address was among
many listed in the TO or CC line? Privacy is a big issue these days among computer
users and having your address displayed in that manner only gives multiple unknown
recipients access to your address and open you up for a mailbox jammed full of
spam!