Do you want to send a copy of an email message to someone without letting the main recipient know you’re doing so? That’s the primary purpose of the Bcc (blind courtesy copy) field, which is available in any Internet-standard e-mail program. It also comes in handy when you want to send an e-mail message to a group of people without broadcasting the entire list of addresses to every recipient. Use the Bcc field for the addresses of all the persons you want to receive your message. Those addresses do not appear in the headers of any message, thus protecting the privacy of your recipients.
Most mail programs allow you to leave the To: field blank. The lack of a recipient can cause spam filters to tag your message as junk mail, however, so I recommend that you use your own address in the To: field instead.
By default, Outlook Express hides the Bcc field, but you can make it visible with just two clicks. From a new message window, pull down the View menu and choose All Headers. In Thunderbird, click the down arrow to the left of the To: field on any address line to choose the Bcc field. In Microsoft Outlook, the option to show or hide the Bcc field is on the View menu when you create a new message.
Ed Bott 