This cutsie graphic going around contains an important lesson. When you send an email to a group using TO or CC, everyone in the group can see everyone else’s email addresses. You might think, So what? We’re all friends.� Yes, but what about when your friend forwards the message on to a few dozen or a few hundred of his friends? Do you really want all of them to have your email address? If any one of those friends-of-friends is infected by a spambot — BINGO, you all start getting spam.
In case you think this is an unlikely problem, it happened to me this Christmas. I received a Merry Christmas email blast from someone I’ve never met, who lives thousands of miles away — a relative of a co-worker. The happy email was addressed to hundreds of people, and all of their email addresses were visible. Shortly after that, I started getting a LOT more spam.
Another reason to use BCC when emailing a group is to prevent an Unsubscribe Storm. �This starts when a large mailing gets some smart-ass, controversial, or off-topic responses. The responders use reply-all, so everyone can see their brilliance. This annoys people who are now getting a lot of messages they don’t want, so some of them also reply to all, saying “Take me off this list”. �At that point, nearly everyone wants off the list, and the volume of messages saying so becomes really alarming.
It sounds funny, but it can get really out of hand. I saw a case where a message like this had a large attachment. The resulting volume rendered heavy-duty corporate mail servers unusable for the rest of the day, and the mess took a while to clean up.
If BCC had been used, then reply-all would only reply to the sender, and no harm would be done.