I had a good discussion in the office with my colleagues today. I had ask one of them to work on an office email etiquette guideline and mentioned that he should include a guideline on bcc: (blind carbon copy).
It is my practice that I do not use the bcc: unless I bcc: all the recipients in my email. My colleague asked me why, and I told him that I have encountered situations where it got awkward when someone did not realise that he was a bcc: recipient and proceeded to send a reply to all the intended recipients.
My colleague did not believe me and insisted that a bcc: recipient will not be able to reply to all except the sender.
He did a test and got his answer.
So, never send an email with bcc: recipients unless all of them are bcc: recipients. If you really need to send an email secretly to someone, send the email proper to the intended recipients first and then forward that copy of email to your secret recipient.