What is SMTP Protocol
Definition – SMTP stands for “Simple Mail Transfer Protocol“, and it works on the application layer of TCP (Transmission Control Protocol) protocol. SMTP protocol helps to send all emails on the Internet, and then Mail Transfer Agent (MTA) forwards your email on appropriate computer. So this method is also known as “store and forward”.
Full form of SMTP is “Simple Mail Transfer Protocol” that system is used in the Computer networking for sending and receiving emails.
SMTP is group of few communication rules that permits to email client such as (Outlook, Eudora, etc) for pushing email messages over the remote email server, and other hand those servers are enabled with SMTP that assist to emails over the identified receiving email server.
SMTP protocol is capable to move one message on one or multiple recipients, and moving emails can enable with (text, video, image or audio).
Architecture of SMTP Protocol
In this SMTP concept, all users use the User Agent (UA) programs such as Outlook, Netscape, Mozilla and more. MTA (Mail User Agent) helps to exchange all messages between both (edges sender and receiver) with using the TCP/IP. System administrator has authority to configure set up of local MTA, so users don’t responsible to move email with using MTA. MTA (Mail User Agent) keeps the queue in pool of messages, if receiver is not presented at that moment then MTA can make to schedule for repeating the delivery of all messages. MTA (Mail User Agent) forwards the emails into mailboxes of users’ local system, and then user agent (UA) can download those messages any time.
Working of SMTP
SMTP protocol’s working is divided into five segments, such as –
Composition of Email – Users compose the all e mail messages, and then they send those composed massages with using of MUA (Mail User Agent). Mail User Agent is software that helps to move and access emails. The email message has two segments such as “body and header”. Body segment contains the main message area, and other side Header enables with sender and recipient address as well as it also contains the main heading of message like as subject of email.
Submission of Email – When users compose email completely then they move the entire email to SMTP (Simple Mail Transfer Protocol) server on the TCP/IP PORT 25.
Delivery of Email – After submission of email, MSA will move messages to MTA. Then Mail Transfer Agent is going to identify the destination domain and IP (Internet Protocol) of recipient’s domain name from “Domain Name System”. After locating the recipient’s domain, MTA makes connection to server for broadcasting messages.
Receipt and Processing of Mail – After receiving the messages by recipient, and then data exchange server forwards that message to MTA (Mail Delivery Agent) which are saved all emails.
Access and Retrieval of Mail – All email are saved in the MDA, and these messages are accessed by the MUS (Mail User Agent).
SMTP Protocol Method
SMTP (Simple Mail Transfer Protocol) is base on the two methods, such as –
End To End – End to End method is implemented in between the multiple dissimilar organizations. In this method, firstly to make contact directly by SMTP client with destination host SMTP then to send the messages destination terminal.
Store and Forward – This method is worked, if exchange the message between same organization. In this method, SMTP client can’t send messages directly to destination point because firstly those messages are stored on the server then their copy of those messages move to destination email box.
Here, we will discuss about few SMTP’s Commands, like as –
HELLO – To find the appropriate path client to server, with qualified domain name, as well as one session is sent at one time.
MAIL – Take decision for sending messages by domain of originator.
RCPT – To find the destination address, and several addressees can be used single RCPT to every addressees.
DATA – Now finally, entire data will be sent frequently line by line.
Components of SMTP
SMTP protocol has mainly three components, such as –
- User Agent (UA)
- Mail Transfer Agent (MTA)
- Mail Gateway
Entire functionality of SMTP protocol is based on these components. Explain below each one –
- Main task of User Agent is to create message, and it makes the envelope then insert that message into envelope. Now finally, Mail Transfer Agent moves this message over the internet.
- SMTP protocol can also allow multiple MTA like as extra MTA attached with sender edge and other MTA linked with receiver edge, and due to use of addition MTA, massive emails can be sent over the internet.
- Without using of TCP/IP protocol, users can send their messages over the internet with using of Mail Gateway. Mail Gateway works as Relay MTA that helps to access all emails.