How is Bcc sent from outlook?

Question

Email

The essence of the question is this - How can a hidden copy be sent to the left addressee?
A simple example, a letter from a client came to the address, after which the left address answered this client's letter.
That is, not the box to which the client sent, but someone intercepted this letter.
Climbed into outlook 2007, there is nothing like that in the rules.
On the hosting where the box hangs is also clean.
Where to look? what are the variations?

Answer 1

well, look in the logs of the mailserver, well, if there was a bcc, then most likely it was added on the client side, unless of course the letter was generated from the form on the site.