The client half of the worked SMTP session — envelope first, headers inside DATA
The client half of the worked SMTP session — envelope first, headers inside DATA
Answer
EHLO client.example.org MAIL FROM:<dana@example.org> RCPT TO:<sam@example.net> RCPT TO:<quiet@example.net> DATA To: sam@example.net Subject: lab notes Numbers attached tomorrow. . QUIT
Two RCPT TO commands, one To: header. The envelope decides delivery and the header decides display, so quiet@example.net appears in exactly one of them — that is BCC on the wire, with no Bcc header anywhere.
RFC 5321; RFC 1939; RFC 3501