Postmaster is a commercial add-on by Objective HTML.

Postmaster is the definitive solution for emailing channel entries within ExpressionEngine. Create beautiful email templates using the live preview, and impose extremely fine levels of control to send emails exactly when you want. Whether it be from the publish entries page in the control, to Safecracker on the front-end, or in a custom application using the channel entries API, Postmaster is the perfect for almost any application.