What is SMTP (Simple Mail Transfer Protocol)? How it Works?

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By Vijay Singh Khatri

Humanity has always relied on communication. The world is shifting toward digital advancements as a result of digital civilization. It’s all because of the effective and quick communication system. Social media apps have emerged as the most popular, fastest, and safest way to communicate with others. Emails, on the other hand, remain an essential part of any corporate business, organization, or personal mode of communication. It has altered how we communicate.

When we talk about corporate communication, we often assume emails for internal or external communication with clients, creating a brand image, generating potential leads, and so on. An SMTP, or Simple Mail Transfer Protocol, server is required to send emails in bulk. This guide will teach you the fundamentals of SMTP and how it works.

What is SMTP?

SMTP stands for Simple Mail Transfer Protocol. Similar to IP or Internet Protocol addresses, SMTP is the main communication network. SMTP is also an important part of the TCP/IP protocol. It mainly works on the idea of “store and forward”. SMTP sends the communication to the requested computer while working with the MTA or Mail Transfer Agent.

Whenever you send an email, it diverts from one MTA to another MTA, and the SMTP controls this process. The simple email communication from the server is only possible due to the Simple Mail Transfer Protocol and its numerous codes that incoporate the whole process. SMTP converts and breaks the message into various parts that only the email servers can understand. SMTP has the potential to send only text, but you can’t send fonts, graphics, or other attachments. It is the reason SMTP is named the “Simple Mail Transfer Protocol.”

What is SMTP Server?

The SMTP server is an application used via mail servers to send, get, and relay outgoing mail between email senders and recipients. Whenever a person sends an email, it is shifted over the internet from one server to the next, utilizing SMTP. An SMTP email is only an email sent using the SMTP server.

However, the SMTP server is utilized mainly to send emails; the SMTP relay can be characterized as moving an email starting with one server and then onto the next. It is primarily used to convey emails, starting with one domain and moving onto the next, which is not the same as the user’s domain. The SMTP relay also helps to tackle many issues, such as email deliverability, IP blocklisting, etc.

Types of SMTP Servers

There are two types of Simple Mail transfer protocol servers;

1. Normal Servers

As stated by the name, a normal server is a common SMTP server that recognizes emails and lines afterward received by the receiver. It is essential to determine the tonne of closed domains that the server deals with. However, if any email rolls in from a substitute domain and a pass-on message are allowed, then it will be forwarded to its destination server. SMTP servers can be utilized as a bidirectional bound service for delivery.

2. SMTP Proxy Servers

Unlike the SMTP servers, proxy servers are not functional, yet they require a real SMTP server to connect to. Clients interface with actual SMTP servers with the help of proxy servers so they can prevent excessive mail, examine their emails, and even change the content.

How does SMTP Server Works?

The SMTP server functions exactly like the fundamentals of our basic email system. It gathers the sender’s email and sends it to the beneficiary’s SMTP server, which is usually the local post office.

Therefore, when you attempt to send an email, for instance, through Gmail to the Yahoo email service, SMTP’s primary job is to move the mail from the source’s mail server to the receiver’s mail server. Eventually, the other recipient that receives and further sends the email to the beneficiary’s end is known to be POP/IMAP.

The message in the email is usually sent using port 25 to an SMTP server created by your client’s mail.

The client and the server start a discussion where the server attests to all the data concerning the transmission of the message, like source, beneficiaries, area, etc. It is important to note that the SMTP language describes only the transmission of the message and doesn’t carry the content of the message body.

If the space in which the recipient has a spot has its record connected with the server, the email is conveyed immediately. The SMTP server passes the message to one other server nearer to the recipient.

Suppose somehow the beneficiary’s server is down or involved. In that case, the SMTP server utilises the backup server: if none of the servers is available, the email is queued, and the movement is retried irregularly, the message will be sent back as undeliverable.

Some basic commands of SMTP

SMTP commands are a bunch of codes that empower the transmission of email from the sender to the receivers or between servers. Below are some basic SMTP commands you ought to know about:

  • HELO or EHLO: It is an essential command for starting the email sending process. The email client recognizes itself as the SMTP server. It is the start of interaction and, for the most part, includes the server sending a HELO command back, complete with its domain name/IP address.
  • MAIL FROM: The source will share code that determines who the mail is from with the identification command. This frames the email address and informs the SMTP server that another exchange will begin. After that, the server resets everything and is prepared to acknowledge the email address. Once acknowledged, it will answer with a 250 OK answer code.
  • RCPT TO: To identify the recipient to whom the email is delivered, the recipient must follow the 250 OK answer code. Once more, the SMTP server answers with a similar code, so it directs one more RCPT TO command that can be sent with an alternate beneficiary’s email address. It can go this way and many times as required, depending upon the number of individuals who will get the email.
  • DATA: The DATA command sets off the data exchange between the client and the server. All of the message substance will be moved to the SMTP server, and then the server will reply with a 345 answer code. The message content is sent to the server. From there, without anyone’s help, the single dot is forwarded in a line to flag the message end. Once it has been acknowledged, it will be prepared to be sent for delivery. In such a situation, the server will forward the 250 OK codes, stating that the message is on the way to the beneficiaries.
  • QUIT: Once the email is sent, the QUIT command is forwarded to the server, cutting off the connection. However, with the successful close, a 221 code will be sent by the SMTP server.
  • RESET: RSET, or Reset Command, is delivered to the server when the mail exchange is required to be stopped. The connection isn’t closed. However, it resets everything and eliminates all past information about the email and its parties. This command is usually used in the event of an error, such as writing the wrong recipient information or needing to restart the whole process.

What is the Need for an SMTP server?

Suppose you are familiar with the concept of SMTP and SMTP servers and how they work. The main question that emerges is why we use SMTP servers, despite having different email services such as Gmail, Yahoo Mail, and others. People use these ordinary email services on a daily basis for mailing and for usual communication. Yet, they have specific restrictions that an SMTP server can bypass. SMTP servers can be utilised to both dribble marketing emails and transactional emails.

Scalability is the primary reason for utilizing SMTP servers rather than other available email providers. Even so, only the dedicated SMTP server can make scaling possible. For instance, you maintain a business and need to send emails in bulk related to your new offers and recognize user activity on the site like password changes, forgotten passwords, and signup processes. To deal with each of these, you want a system that should not be possible by sending emails from a browser that isn’t a choice.

What are the Advantages of SMTP Server?

Normally, the in-build SMTP server is provided along with the hosting web service. Hence, you can create free SMTP servers and email accounts for your organization linked with your web hosting service.

Even though you can get a free in-built SMTP server with the web hosting service at an affordable price, it would be wise to utilize external SMTP servers since the in-built SMTP servers have certain restrictions and also lack performance. Restrictions include:

  • Less mail speed, which makes sending and receiving emails quite slow, especially if you are utilizing shared web facilitation.
  • Moreover, the SMTP protocols are vulnerable to being hacked. The inbuilt SMTP with hosting services is generally missing due to reasonable prices.
  • The in-built SMTP has cheap security measures against online hacking.

In contrast, using a third-party or external SMTP server can benefit you in numerous ways, as outlined below:

Fast Speed

An external SMTP server is designed to offer fast speed in the entire process of sending and receiving emails. It will be handled smoothly by the SMTP, especially if you run a business and need to send and receive emails in bulk.

Better deliverability

Your email will be secure and delivered without interruptions or delays with the help of an external or specific SMTP server. You could also use a free SMTP server, such as Amazon SES, which is very easy to set up and use. These servers also prepare a monthly report with details on low and high and other critical data that may be important to you.


To summarise, emails and SMTP servers are critical to the operation of any organization or business. SMTP and SMTP servers are capable of being used in general email services.

The SMTP server guide mentioned above would have helped you provide a comprehensive understanding of how SMTP works and its effectiveness in meeting the communication needs of organizations for various purposes. Before settling on a specific SMTP server, it is a good idea to spend some time gathering information about the various types of SMTP servers available on the market. Before deciding on an effective communication method, consider your needs.

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