If you've never been a recipient of a mistaken reply-all, you're either very lucky or you don't use e-mail much.

It's a useful tool that is also one of the banes of our electronic lives, as well-meaning people blast dozens or hundreds of recipients with boring (or, worse, sensitive) replies that should be directed to one person. Microsoft has devised a free tool for Outlook that lets users create messages that keeps recipients on the same Exchange domain from using reply-all or forward. It's simple to use and doesn't require installation on the recipients' end. Here's how to use it.