What is the difference between BCC and undisclosed recipients?

BCC (Blind Carbon Copy) is the actual email feature that hides recipients from one another. Undisclosed Recipients is not a separate function but rather a display label that appears when an email client shows a generic placeholder because all real recipients were placed in the BCC field.

In practice, a sender often puts their own address (or a placeholder like Newsletter) in the To field and adds everyone else in BCC. The result is that no one can see who else received the email, and some clients display Undisclosed Recipients to indicate that.

It is like sealing a cargo manifest and labeling the shipment simply "To: Valued Customer." BCC is the act of sealing the manifest, while Undisclosed Recipients is the printed label on the crate.