While not yet an Add-on, it can be added to your Google Sheets as a Script.
postBlaster is another wonderful Google Script form the brains behind the New Visions for Public Schools. postBlaster can be set up to send emails to anyone you choose when a post is made to a Google Site Announcements Page.
We use it here to keep everyone informed about any announcements made from the principal’s pages. Each time a principal posts to their page, postBlaster automatically grabs the content and emails it out to my custom list in a neatly formatted email. In our case we email to a Google Group so everyone in district gets it, but it can be individuals as well.
Intrigued? Click the link and try it out yourself.