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What is the full form of SMTP


SMTP: Simple Mail Transfer Protocol

SMTP stands for Simple Mail Transfer Protocol. It is a standard protocol on a TCP/IP network for sending emails through servers from one computer to another computer. It is a part of the application layer of the TCP/IP protocol, which makes possible to send email messages over the internet to one or more recipients. So, it is used when an email is sent from an email client, such as Outlook Express or Gmail, to the recipient using email servers.

SMTP Full Form

SMTP moves your email across networks through a process called "store and forward." It works in coordination with Mail Transfer Agent (MTA) to send you mail to the right computer and email inbox. It decides how an email will move from one computer's MTA to another computer's MTA. The message moves in steps from its origin to its destination, and at each step, SMTP does its job.

SMTP is developed and maintained by the Internet Engineering Task Force (IETF). It is also known as RFC 821 and RFC 2821. It uses port 25 and sets up communication rules between servers and works by starting a session between the user and server, whereas Mail Transfer Agent (MTA) and Mail Delivery Agent (MDA) provide domain searching and local delivery services, respectively. It functions when computers are connected with Internet Service Providers (ISP). The ISP servers then deliver the mail to the recipients having internet service.

Components of SMTP:

  • Mail User Agent (MUA): It is the local user or client-end utility that allows to receive and send mail.
  • Mail Submission Agent (MSA): It is the server which receives from MUA and cooperates with the MTA for delivery of the mail.
  • Mail Transfer Agent (MTA): It receives incoming mail from local user and forwards it for delivery. More than one MTP can be involved, as a client or server to transfer the mail.
  • Mail Delivery Agent (MDA): It delivers the mail to the local recipient's mailbox.

How SMTP Works:

The working of SMTP is a three-step process and is based on the client/server model. In the first step, an email server sends the email (message) from an email client such as Gmail, Outlook, etc., to an email server using SMTP; in the second step, the email server using SMTP sends the email to the receiving email server. In the third step, the receiver server uses an email client to download incoming mail via IMAP and place it in the inbox of the recipient.

Let's understand in an easy way:

  1. Submission of Mail: The mail client submits the completed mail to the SMTP server by using SMTP on TCP port 25.
  2. Delivery of Mail: The SMTP server divides the recipient mail address into two parts: recipient's username and domain name. For example, rocky@gmail.com, where "rocky" is the username of the recipient and "gmail.com" is the domain name.
    If the domain name of the sender and recipient are same, the SMTP server directs the email towards POP3 server for domain using the delivery agent. If their domain names are different, Mail Submission Agent (MSA) sends the mail to the Mail Transfer Agent (MTA), which searches the MX record from the Domain Name System to obtain the recipient's domain. The MX record contains information about the user's domain and IP address. Once, the domain is located, MTA connects to the exchange server to transfer the mail.
  3. Receipt and Processing of Mail: After receiving the incoming message, the exchange server transfers the message to the incoming server (Mail Delivery Agent), which holds the mail until the user gets it.
  4. Access and Retrieval of Mail: The email stored in the MDA is retrieved by using MUA (Mail User Agent), which can be accessed by using login id and password.

Benefits or Advantages of SMTP:

  • It makes it possible to communicate via mail messages over the internet from one computer to other computers.
  • It is a reliable method of communication. It resends the messages which are not sent successfully until the recipient receives it.
  • It also allows bulk email marketing in which one can send emails to a large number of recipients at the same time.

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