BCC and email privacy

When you email more than one person, your email program gives you three address boxes: To, Cc and Bcc. Addresses typed into To or Cc appear in the header that every recipient receives. An address typed into Bcc (blind carbon copy) is hidden from the other recipients.

What each recipient can see

So the To and Cc lists are visible to all, the Bcc list is visible only to the sender, and the people in Bcc cannot see each other. If a recipient replies to everyone, only the To and Cc addresses are contacted.

Why this protects personal data

An email address identifies a living person, so it is personal data. Imagine you are collecting raffle prizes for a school charity fair and you email 15 local shops to ask. If every address goes in To, each shop opens a message listing the other 14 and learns who else you asked; some owners may not want a rival to know they are helping.

Putting the 15 addresses in Bcc means each shop sees only its own address and yours, so no address reaches anyone with no reason to hold it. That applies the protected principle: personal data is kept secure and seen only by the people who need it. As a rule, use Bcc for a group who do not know each other, and To when everyone may need to reply to all.

Bcc hides addresses, not the message: everyone still receives the same email and can forward it, so it does not keep the contents secret. It also works for a single hidden address. A student emailing a leisure centre about a cancelled swimming lesson can Bcc a parent, so the parent gets a copy while the centre never collects the parent's address.