Not much is stated by the author of this book in the first book that helps understand when this book was written. But evidence in the book points to about 475-450 B.C., after the Israelites returned to Jerusalem and rebuilt the temple. Yet long enough after to have the people and the priests turn back towards their apathetic worship in the temple.
Nor is much known about the author. Some even question if his name is really Malachi, or if it was an anonymous prophet that was called “my messenger” by the Lord (Malachi literally means “my messenger.”) Regardless, the prophet was known as Malachi, and his words were the Words from the Lord.
The book is highlighted by six disputes that the Lord has with His chosen people. These disputes follow a fairly standard format: First the dispute from the Lord, then the response by the people denying the accusation, and finally proof from the Lord backing the accusation. It’s amazing how this accusations from God could be leveled against the 21st century church as well.