Learn in the textbookMail, File, and Operations Protocols
DefinitionSMTP is the protocol for sending email and relaying it from one mail server to another.
ExplanationA mail server holds users' mail, delivers it onward, and stores mail that arrives. SMTP is used both on the leg from the sender's device to a mail server and on the legs where mail servers pass the message along to its destination.
AnalogyIt covers dropping a letter in the postbox and the post offices passing it along to the office in the recipient's area. It does not include the recipient going to pick up the mail held at that office.
Memory hookIt stands for Simple Mail Transfer Protocol, and "Transfer" means to carry or move. Read it as the protocol whose job is moving mail.