Which of the following would be used to send messages using the SMTP protocol?

 Email software would be used to send messages using the SMTP protocol. SMTP stands for Simple Mail Transfer Protocol, which is a network protocol that enables the transmission of email messages from a client to a server or from one server to another. Email software is an application that allows users to compose, send, receive, and manage email messages using SMTP or other protocols, such as POP3 or IMAP. Examples of email software include Microsoft Outlook, Gmail, Yahoo Mail, etc. References : The Official CompTIA IT Fundamentals (ITF+) Study Guide (FC0-U61), page 166.