SMTP
SMTP (Simple Mail Transfer Protocol) is a standard internet protocol used for sending and relaying email messages between mail servers. It operates on TCP port 25 (or 587/465 for secure variants) and defines the rules for message formatting, transmission, and error handling in email delivery. SMTP is a text-based, client-server protocol that handles the 'sending' part of email communication, while other protocols like POP3 or IMAP handle retrieval.
Developers should learn SMTP when building applications that need to send email notifications, transactional emails, or integrate with email services, such as in web applications, marketing platforms, or system monitoring tools. It's essential for implementing custom email servers, debugging email delivery issues, or working with email APIs (e.g., for authentication or spam filtering), as it provides low-level control over email transmission and is widely supported across systems.