Since most of the subscribers were wondering how the heck they got on the "newsletter" to begin with, their automatic reaction to the offensive message is to reply with rude, and sometimes threatening, demands to be unscubscribed. The server then relays all the rude replies to all the subscribers.
The replies from the subscribers who receive the rude replies run from legalistic to tearful, to even more rude and threatening than the original rude replies.
Perhaps one subscriber out of a hundred will recognize that none of the offensive and rude messages were intended specifically for himself. He may even try to persuade the rioters to calm down, but few of them will notice his pleas for reason amongst all the crap in their inboxes.