Easy internet access increases the number of emails sent and received yearly. Statista reports estimate that by 2026, 392.5 billion people will send and receive email worldwide daily. 

People consider email to be the most reliable communication medium; that’s why it breaks down all geographical barriers so quickly. From small businesses to global corporations, email is used to stay connected with customers and teams. It helps them spread information-related products and services to the appropriate team and potential customers. However, have you ever considered how your messages are sent from you to intended recipients? 

Well, there’s a reliable component that ensures our emails are delivered safely. That component is named Simple Mail Transfer Protocol (SMTP). So, what is SMTP? How does it work? And how is it essential for effective communication? This guide will explore everything from SMTP meaning to its key concepts, workings, and more. 

What is SMTP?

SMTP is a communication protocol that enables the transmission of email from one user to another over the Internet. SMTP first came into use in the early 1980s and became immensely popular after that. It is a universal set of rules that allows the transfer of email between the sender and the recipient.

SMTP is a push protocol used to send mail, but for retreating the mail, POP (post office protocol) or IMAP (internet message access protocol) is used. 

SMTP ensures that emails are properly formatted, addressed, and delivered to the targeted destination. It facilitates effective email routing from the sender's email client to the receiver's email server. SMTP provides a reliable and efficient way to send email messages, using port 25 (for SMTP relaying) and port 587 (for encrypted email transmissions using SMTP Secure (SMTPS). 

Types of SMTP Model

There are two main types of SMTP:

1. End-to-End SMTP

This concept is used to communicate among various organizations. When an organization has to establish communication, end-to-end SMTP serves as a bridge between them. In this model, the client initiates the communication session. The client's request waits for the receiver's SMTP, and the receiver receives the communication signal.

2. Store-and-Forward SMTP

Unlike end-to-end SMTP, this model is mainly used for internal communication within an organization. Organizations send emails using this model. The server saves the email that it receives from various organizations. The store-and-forward model does not transmit mail until it has saved a copy, which is why it is used to improve the organization’s server security.

Components of SMTP

Here are the components of SMTP:

• Mail User Agent (MUA): Application for sending and retrieving emails, creating messages for transfer to the mail transfer agent (MTA).
• Mail Submission Agent (MSA): Receives mail from MUA and interacts with MTA for transfer of the email.
• Mail Transfer Agent (MTA): Software that transfers mail between systems using SMTP.
• Mail Delivery Agent (MDA) or Local Delivery Agent: A system that delivers mail to the local system.

What is an SMTP Server (SMTPS)?

There are two types of SMTP server: 

Regular SMTP Server

It is intended to send regular personal emails. These servers are often owned by email providers such as Gmail, internet service providers such as AT&T, or web hosting companies such as MailChimp. They typically have severe daily email-sending limits. 

Dedicated SMTP Server

This type of server is particularly handy because it can manage large numbers of emails. Many businesses use such servers for transactional or marketing emails. 

Working of SMTP

Source

Here’s how the Simple Mail Transfer Protocol (SMTP) works:

Communication Between the Sender and Receiver

• The sender’s email client (like Gmail or Outlook) prepares the message and sends it to the Mail Transfer Agent (MTA).
• The MTA is responsible for transferring the email across the network to the recipient’s MTA.
• To send an email, your system needs a client MTA.
• An email needs a server MTA to receive it.

SMTP Connection (using Port 25)

• To send and receive emails, you need to set up an SMTP server.
• Email clients can then be configured to connect with this SMTP server.
• When you click “Send” on an email, an SMTP connection is established between the client and the mail server.
• This connection uses the Transmission Control Protocol (TCP) as its transport protocol.
• The client initiates the process with a specialized “Hello” command (HELO or EHLO).

Command Transmission

• Commands transmitted by the client give instructions to the server once the SMTP connection is active.
• These commands include the sender’s and recipient’s email addresses, as well as the email’s content.
• The MTA checks if both addresses are from the same domain (e.g., gmail.com).
• If not, it uses the Domain Name System (DNS) to identify the receiving domain and transmit the email accordingly.

 Email Data Transfer

• Email is sent through a series of requests and responses between the client and the server.
• The client sends the server a series of commands along with the email’s content (header, body, and attachments).
• The header contains information like sender, recipient, and subject, while the body contains the actual content.
• The server runs a Mail Transfer Agent (MTA) program, which checks the recipient’s email domain.
• If the domain differs from the sender’s, the MTA queries the Domain Name System (DNS) to find the recipient’s IP address.

 Mail Transfer Process

• The initial mail server is usually not the final destination for the email.
• It repeats the SMTP connection process with another mail server, which does the same.
• This process continues until the email reaches the recipient’s inbox on their email provider’s mail server.

Receiving Emails

• The user agent (email client) on the recipient’s side checks for new emails at regular intervals.
• If a new email is received, it notifies the user.
• When the user opens the email, they can view a list of emails and their brief descriptions.
• By selecting an email, the user can read its full content.

Basic SMTP Commands

Here are some basic commands used in SMTP to communicate with email servers:

Pros and Cons of SMTP

Some of the most common pros and cons of SMTP are given in the below table:

Comparing Email Protocols: SMTP vs. IMAP vs. POP3

A comparative table between the top most used protocols for effective email communication:

Learn more about how to buy SMTP Servers.

Neo: A Reliable SMTP Service Provider

Neo is one of the best free SMTP service providers that offers reliable email delivery. It helps marketers manage their email marketing efforts. With the Neo SMTP service, you can create emails and manage contacts, along with an email delivery engine that simplifies email delivery. Neo’s SMTP server includes several high-tech tools used for managing mailing lists and setting up email campaigns. 

The most crucial feature of Neo SMTP is bulk emailing. It enables you to send bulk emails in just a few minutes. These emails include everything from welcome and newsletter emails to configuration emails and more. Neo provides a reliable email service and ensures that all of your mail reaches its final destination.

Moreover, Neo offers a cloud-based email service that allows you to create newsletters and manage lists from the desktop. It will also offer a cloud email tracking service that helps create reports on the email campaign's performance. Other features like generative AI and the "Advanced Mass Sender" (AMS) offered by Neo will assist you in writing and improving your online presence.

Wrapping Up,

In the end, with the wide use of electronic email for commercial or personal services, there is a very high demand for authentication and confidentiality. SMTP is one of the most well-known and implemented protocols that allow us to exchange electronic messages via the Internet. This universal server identifies the sender, recipient, and message and declares what kind of communication they are expecting. Therefore, SMTP ensures everything from bulk marketing email delivery to preventing messages from being spam. It can also help to detect error messages, spam, and phishing attacks. 

Frequently Asked Questions

1. What is an email protocol?

An email protocol is a set of rules that allows transmitting emails to and from the server. It facilitates communication processes by exchanging emails between the sender and recipient. The primarily used email protocols are IMAP, POP3 (inbound), and SMTP (outbound).

2. What is SMTP?

SMTP stands for the Simple Mail Transfer Protocol, which is used to send emails via the Internet. It has been a widely used protocol all over the world for four decades. It enables the user to send the bulk of the email to the specified destination with the help of a message transfer agent.

3. Is SMTP suitable for sending bulk marketing emails?

Yes, SMTP can be used for sending bulk emails, but you must follow email service provider guidelines. It ensures proper authentication and follows best practices to avoid being marked as spam. 

4. What’s the distinction between SMTP and an email client?

SMTP is a protocol for sending emails, while an email client is a software application that allows users to manage and access their email accounts. They are different components of the email communication process.

5. Are there any alternatives to SMTP for email delivery?

While SMTP is a dominant protocol for email delivery, alternative protocols like Microsoft Exchange’s MAPI (Messaging Application Programming Interface) and various proprietary protocols exist for specific email systems.

6. Can SMTP be used to receive incoming emails?

No, SMTP is primarily designed for sending emails. To secure emails, you typically use protocols like POP (Post Office Protocol) or IMAP (Internet Message Access Protocol).