Bcc: stands for "blind carbon copy." This is similar to the Cc: feature, except that Bcc: recipients are invisible to all of the other recipients of the message (including other Bcc: recipients). For example, if you send a message To: email@example.com and Bcc: firstname.lastname@example.org, then johndoe will see himself as the message's only recipient, while janedoe will see that you have also sent the message to johndoe. The Bcc: field is useful in instances when you don't wish to share your recipients' email addresses with everyone who receives your message.
To send a message, you must always specify at least one recipient in the To: field. If you don't, an error message will appear when you attempt to send the message.
Please note: Sending unsolicited mail, or spam, is a violation of the Yahoo Terms of Service and will not be tolerated.