Simple Mail Transfer Protocol (SMTP)
SMTP Protocol (Simple Mail Transfer Protocol) is a collection of communication rules that permit the software to send an electronic mail (email) over the internet. Email is one of the most up-coming and invaluable services on the internet. Most systems utilize SMTP Protocol as a technique to transfer mail from one customer to another. SMTP Protocol is used in sending the email and works as a push protocol while IMAP (internet message access protocol) or POP (post office protocol) is used in retrieving these emails at the receiver’s end. SMTP falls under an application layer protocol.
When an email wants to be sent, the user starts a TCP connection to the SMTP server and then transmits the mail through the connection. The SMTP server is continually on listening mode. The moment it listens for a TCP connection from any user, it begins a connection on that port. After effectively creating the TCP connection, the mail gets sent immediately. SMTP Protocol transmits messages based on e-mail addresses. It offers a message interchange between clients on the same computer or on different devices.
It can also perform the following tasks:
- It can transmit a message to more than one recipient.
- It can attach text, video voice or graphics in the message.
- It can transmit messages on networks external to the internet, as well.
Understanding of SMTP Protocol
- The main idea behind the SMTP Protocol is to set up communication guidelines among servers. The servers identify themselves and announce the kind of communication being done. Servers also handle errors like incorrect email addresses. For instance, if the recipient address is incorrect, then the recipient server responds with an error message.
Normally, SMTP is integrated into an email application and consists of four main components:
- Mail user agent (MUA)
- Mail submission agent (MSA)
- Mail transfer agent (MTA)
- Mail delivery agent (MDA)
SMTP begins a session between the MUA, which is the user and the MSA, which is the server. MTA and MDA are used for searching the domain for addresses and for local delivery services.
Commands Of SMPT
Let us look at a few SMTP Commands:
- HELO – This command is used in identifying the user and the full domain name, which is transmitted only once per session.
- MAIL – This command is used in initiating a message transfer.
- RCPT – This command comes after MAIL and is used in identifying the fully qualified name of the recipient. For multiple recipients, we use one RCPT for each of the recipients.
- DATA – This command is used to send data one line after the other.
Types of SMTP Protocol
The SMTP model can be of the following two types:
- End-to-end model
- Store-and-forward model
The end to end design communicates between different organizations while communicating within the organization is the warehouse and forward model. To submit an email, the customer contacts the destination”s SMTP immediately. The SMTP server keeps the email until the receiver’s SMTP effectively receives it. The SMTP customer initiates the meeting and the SMTP receiver reacts to the petition for the meeting.
How does SMTP Protocol Work?
Let us look at the working of SMTP to get a better understanding.
Composition of Mail:
Initially, the sender composes an e-mail message with the help of a Mail User Agent (MUA) and then transmits the e-mail. MUA helps in sending and receiving mail. The email message consists of two parts, namely the body and the header. The body comprises of the main portion of the message while the header comprises of the subject, which is a one-line description of what the body holds and the sender and recipient address information.
Submission of Mail:
The customer utilizes the Simple Mail Transfer Protocol after the structure of the document is complete and sends the completed document to the server on TCP channel 25.
Delivery of Mail:
E-mail addresses contain the recipient’s username and the domain name. In firstname.lastname@example.org, “abc” is the username of the receiver and “gmail.com” is the name of the domain. If the recipient”s domain name is different from the sender’s domain name, then MSA will send the letter to Mail Transfer Agent (MTA). To transmit the email, the MTA searches for the target domain. It looks in the Domain Name System (DNS) to find the target domain. Once the record is found, MTA connects to the server to transmit the message.
Receipt and Processing of Mail:
After the server receives the message, it sends it to the Mail Delivery Agent (MDA), which keeps the e-mail until the user retrieves it.
Access and Retrieval of Mail:
The email stored in the MDA is retrieved by logging into the MUA, with the help of a username and password of the MUA.
Advantages of SMTP Protocol
- SMTP delivers the easiest form of communication by emails among several computers in a specific network.
- SMTP is made from a simple platform, making it easy and quick to send emails.
- SMTP presents reliability for outgoing email messages, in a way that if a message is not sent successfully, then the SMTP server tries to re-send the same message up until the message is sent successfully.
- SMTP helps to have a committed server to manage outgoing email messages in organizations.
- It is easy and simple to connect to SMTP. It offers an easy installation.
- SMTP connection has no limitations and can be used to connect to any system. All we have to do is incorporate the SMTP information.
- It doesn’t include any development from our end.
SMTP provides the easiest solution to send emails and messages to people all over the world. Bulk emailing is possible only via SMTP servers and it is one of the most money-friendly means of sending out emails to a vast number of people at a time.
This has been a guide to the SMTP Protocol. Here we discussed the Working, command, Types, and Advantages of SMTP. You can also go through our other suggested articles to learn more –