Bcc

What it means

Bcc recipients are given to the server in the envelope but kept out of the header the other recipients see. RFC 5322 describes three ways to do it: remove the Bcc field from every copy; send the To and Cc recipients a copy without it and the Bcc recipients a separate copy that includes it; or send a Bcc field with no addresses, to signal that blind copies were sent.

Because their address is usually absent from the copy they receive, Bcc recipients get mail that appears addressed to someone else, and out-of-office responders following RFC 3834, which answer only when the recipient is listed in To, Cc or Bcc, will usually stay silent. Sending a newsletter by Bcc from a personal mailbox also runs into per-message recipient limits; sending one message per recipient avoids both issues.