When you want people to know your message needs urgent attention, set the message as high importance. If the message is just an FYI, or if you’re sending mail to colleagues about a non-work related topic, set the low importance indicator.
Click New Email to compose a new message.
In the Tags group on the Ribbon, select High Importance or Low Importance .
In most email programs, the recipients see a special indicator in the message list or headers.
On the ribbon, you can tell when importance is set by whether the button is highlighted.