This article was first written in June 2004 for the BeezNest technical website (http://glasnost.beeznest.org/articles/131).
You should always avoid to send e-mails to many recipients at the same time with their address in the To: or Cc: field.
The reason is that if you use Bcc:, any recipient will not be able to see other’s e-mail address.
Why would you want that?
Because many viruses on the Internet these days know how to go into your e-mail archives and search for the e-mail addresses that you can see too. If you use To: or Cc:, the Windows-running PCs of the recipients become potential war-machines ready to attack any others’. If you use Bcc:, the others’ addresses won’t appear into others’ e-mail, and you are safe to spam and viruses as well as the bad guy(tm).