I'm not using that particular combination ... but in the past when I have
BCC'd someone, I had to click on Message Details (or Show Original or
whatever it's called in your program, that reveals the full headers or the
full raw email message) of my Sent message, in order to see that. It should
(well, it might) be somewhere in the headers of the sent message, but not in
any of the copies that they receive.
Andy