Have you ever gotten emails with hundred recipients in the “To” field? What did you think about sender of such messages? Didn’t you feel irritated that the sender did not take the time to send you an individual message? Do you just delete such messages as spam? Of course, the alternative is sending a message with all the recipients in the BCC field so that they do not see each other, but that is not much better, as recipients usually simply ignore anything that is not addressed personally. On top of that, spam filters are perfectly capable not only of sending the message to the Junk Mail folder, but also blocking the sender.