A blind carbon copy (BCC) is a way of sending an email where the recipients in the To and CC fields don't know that someone else has been copied on the message. However, it is possible to detect if someone has been blind copied on an email. One way to do this is to look at the source code of the email and look for the BCC field. Some email clients also provide the option to view the BCC field in the message header. Additionally, if the recipient of the BCC accidentally "replies all" or "forwards" the email, it may become apparent that another person was included on the message. It's important to use BCC responsibly and only when necessary to protect the privacy of recipients.