This is an invaluable setting if you want to hold meetings or do work at certain times without being alerted to calls ringing on your extension. There are several options for what happens to a call when it tries to contact a line on which the Do Not Disturb feature is activated.
These include redirecting to another extension, such as that of a secretary, giving the call a busy or Do Not Disturb signal, or forwarding the call to an automated recorded message.
It’s up to the owner of the line how the call is routed. You can choose to be alerted visually that a call is trying to get through or receive no notifications at all. Whether the call makes it to your voice mailbox or is forwarded to another phone is completely up to you.