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Write short note on SMTP.

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SMTP, or Simple Mail Transfer Protocol, is a standard communication protocol used for sending and receiving electronic mail (email) on the internet. It is an essential part of the email delivery process, responsible for transferring outgoing emails from the sender's mail server to the recipient's mail server.

Key Features and Functions:

  1. Message Transfer:

    • SMTP facilitates the transfer of emails between mail servers. When you send an email, your email client uses SMTP to communicate with your email provider's server to transmit the message.
  2. Transmission Rules:

    • SMTP follows a set of rules for the transmission of emails. These rules dictate how the email message should be formatted, the information required in the message headers, and the commands used for communication between servers.
  3. Communication Model:

    • SMTP operates on a client-server model. The email client acts as the client, initiating communication with the server, which is responsible for sending or relaying the email.
  4. Port Number:

    • SMTP typically uses port 25 for unencrypted communication. For secure communication, SMTP over TLS (SMTPS) uses port 587. SMTPS provides encryption through Transport Layer Security (TLS) to secure the email transmission.
  5. Authentication:

    • SMTP servers may require authentication to ensure that only authorized users can send emails. Common authentication methods include username and password verification.
  6. Message Format:

    • SMTP defines the structure of email messages, including the header and body format. The header contains information such as the sender, recipient, subject, and date, while the body contains the actual content of the email.
  7. Relaying:

    • SMTP supports the relaying of emails through multiple servers. For example, if the recipient's mail server is not directly reachable, intermediate servers can relay the email to its destination.
  8. Limitations:

    • SMTP is primarily concerned with the transmission of emails and doesn't handle tasks such as email storage or retrieval. Other protocols like POP3 (Post Office Protocol) and IMAP (Internet Message Access Protocol) are used for those purposes.


  • When you send an email through your email client (e.g., Outlook, Gmail), the client uses SMTP to communicate with your email provider's server. The SMTP server then routes the email to the recipient's email provider, where it can be retrieved by the recipient.

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