E-Mail and Moral Luck

A friend of mine is an administrator and we got to talking about the conundrums that can surface regarding listing someone in the bcc: slot, the blind courtesy copy (or for those old enough to remember carbon paper -- the blind carbon copy). The idea is that you are a member of the list of recipients for that message and all others for which "reply to all" is used, but no one other than the original sender knows that you are privy to the communications.

It seems to give rise to two classes of moral concerns. First, are the concerns of the visible recipients. Is it ok to even use the bcc:, to correspond with someone without letting them know who else is reading along and who else they may be sending potentially sensitive or embarrassing information to? Is it enough that the visible recipients know that someone might have been bcc'ed on the message?

Second, what are the responsibilities of the person bcc'ed? You now seemingly have a confidence to keep, yet unlike making a promise you never agreed to accept this moral obligation. This is what Bernard Williams calls moral luck, ethical claims on you that arise by happenstance, not of your own intentional doing. What is entailed by the responsibilities of being bcc'ed? Suppose you have a contribution to the conversation that would be important, is it wrong to send an e-mail to someone on the visible list "I don't know if anyone has talked to you about this, but it might help to know that..." Suppose you write the message so that it in no way is evident that you've been inside the conversation that has been happening? Do you have to request that the bcc'er release you from your hidden status to join the conversation when he or she didn't ask you when assigning it? Should someone be able to lay this ethical burden on your shoulders without your agreeing to it and how heavy is this burden anyway?