Bcc is defined in RFC 822 and supported by most e-mail

systems. A normal, non-blind "CC" header would be visible to

all recipients, thus allowing them to reply to each other as

well as to the sender. According to RFC 822, the addresses

listed in a BCC header are not included in the copies of the

message sent to the recipients. RFC 822 says BCC addresses

may appear in the copy sent to "BCC" recipients themselves

(though this would be unusual).