SMTP, or Simple Mail Transfer Protocol, is an Internet standard communication protocol used for sending and receiving email messages over a network such as the Internet
. It operates at the application layer and uses Transmission Control Protocol (TCP) connections, typically on ports 25, 465, or 587, to reliably transfer email data between mail servers and from email clients to servers
. SMTP follows a client-server model where an email client (the sender) connects to an SMTP server to send an email. The server then relays the message to the recipient’s mail server, potentially passing through multiple servers until it reaches the destination
. The protocol uses a series of text-based commands and responses to establish the connection, specify sender and recipient addresses, and transmit the message content, which includes headers and body
. SMTP itself is designed primarily for sending emails, not retrieving them; protocols like IMAP or POP3 are used for email retrieval
. It supports extensions for authentication, encryption (via SMTPS using SSL/TLS), and internationalized email addresses to enhance security and functionality
. In summary, SMTP is the fundamental protocol that enables email transmission on the Internet, ensuring messages are routed from the sender’s client or server to the recipient’s mail server reliably and efficiently
