SMTP and POP3 are the most likely network protocols that will be used when sending and receiving Internet email. SMTP stands for Simple Mail Transfer Protocol, which is a protocol that enables the transmission of email messages from a client to a server or from one server to another. SMTP is used to send outgoing email messages. POP3 stands for Post Office Protocol version 3, which is a protocol that enables the retrieval of email messages from a server to a client. POP3 is used to download incoming email messages. Reference : The Official CompTIA IT Fundamentals (ITF+) Study Guide (FC0-U61), page 166.