in message
When you receive an email, is it possible to see if anyone's been
BCc'd on it?
What do you think is the point of using the BLIND Carbon Copy (Bcc)
field in your e-mail client?
The To, Cc, and Bcc fields displayed in your e-mail client are not
directly used to specify the recipients of your e-mail. Instead your
e-mail client compiles an aggregate list of recipients from the To, Cc,
and Bcc fields. Then it issues a RCPT-TO command to the mail server for
each recipient following by one DATA command for the content of your
message. So if you have 10 recipients in total in the To, Cc, and Bcc
fields in your e-mail client, your e-mail client would issue 10 RCPT-TO
commands and 1 DATA command.
Only if the e-mail client were broken, hacked, or someone's custom
application would it include the Bcc field in the data of your message
to include in the DATA command used to give your message to the sending
mail server. E-mail clients should be not be inserting the Bcc line in
the body of the e-mail (the part referred to as the headers); otherwise,
every recipient could see it. Some mail servers will strip it out if
found in the content pushed to it by the DATA command.
In fact, because RCPT-TO commands are used to specify the recipients,
you won't know if anyone was listed in the Bcc field in the sender's
e-mail client even if the To and Cc fields were completely blank. Those
fields are not used to specify the recipients. A sender, for example,
could compose an e-mail (the part that gets sent by the DATA command)
and read a mailing list from some separate file to compile the list of
RCPT-TO commands. That's how listservers work to spew out bulk mail.
The sender can put whatever they want in the To and Cc fields in the
*data* of the message but that doesn't mean that list are the recipients
of that mail (and why you can get spam where you were never listed in
the To or Cc fields).
