<begin soap box rant>
Time and time again I find myself having to email people to remind them about how and when to use BCC when sending out correspondence to a huge group via email.
The main rule of thumb I tell the senders is that if dialog is not needed between everyone on the email and it is basically and FYI communication, then everyone does not need to see everyone’s email address. This is especially true for news letters from churches, schools, and other organizations.
In a corporate world this is especially important. If you are emailing out to a large list of people, even using a distribution group such as “ALL IT”, you should still use BCC to avoid the “REPLY TO ALL” scenarios.
In the non corporate environments, one should also consider if you have the permission of the people to share their email addresses. When people sign up for communication from a church, civic organization, school, doctors office etc, they expect a certain level of privacy. Turning around and sharing their personal email address with dozens or hundreds of complete strangers is a quick way to lose their trust in you.
According to wikipedia “BCC is often used to prevent an accidental “Reply All” from sending a reply intended for only the originator of the message to the entire recipient list”