Internet email using the SMTP protocol is usually quite fast, and always free of charge. SMTP is the choice for environments where messages are not as important, and their assured delivery is not of the utmost importance.

Since SMTP is a store-and-forward message delivery system, you cannot always rely on its speed, and failure conditions in the path to message delivery can sometimes occur. For non-critical message delivery, however, it is the logical choice due to its wide-spread use and zero-cost overhead.