Hi Karl,
Thanks for your response and explanation. May I be so bold as to say, I think this way to handle BCC is just plain wrong. If my intent in using BCC in the first place is to hide the BCC list from the TO and CC list, why would a simple response, EITHER Reply or Reply All, reveal the BCC list to some or all of the other recipients, and the TO and CC lists to the BCC recipients? Not clear thinking by the design team. Perhaps they should be introduced to the concepts of "privacy" and "the need to know". As it stands, BCC is useless and deceptively misrepresented.
As the sender, I don't have the option to disallow responses from BCC recipients, so you're telling me the only option to keep them separate is to send the message to each recipient individually? How efficient is that?
TL;DR? This stinks.