What is SMTP (Meaning), and Why It Matters for Email Communication?

June 3, 2024
14 Minutes
Modified on:
June 3, 2024
Written by:
Swati Bucha
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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


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:

Command Function
HELO Identifies server
MAIL (MAIL FROM) Initiates the mail transaction (Sender’s email address)
RCPT (RCPT TO) Identifies mail recipient (Receiver’s email address)
SIZE Informs the server about the size of the email in bytes
DATA Initiates mail data transfer
RSET Aborts the current mail transaction
NOOP Receiver returns OK. Used to test the server connection
QUIT Close the connection
VRFY Verify recipient exists
SEND Delivers message to one or more terminals
SOML Delivers messages to one or more terminals or mailboxes
SAML Delivers messages to one or more terminals or mailboxes
EXPN Expand mailing list addresses
HELP Requests help info from the receiver
TURN Ask the receiver to take a role as a server
AUTH To extend the security by authenticity the client to other servers using the username and password

Pros and Cons of SMTP

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

Pros Cons
It allows users to send email in bulk. Fear of data breach
It sends emails in different geographical locations. Firewalls can block the well-known SMTP protocol.
Cost-effective If the message exceeds a specific length, SMTP may reject it entirely.
Reliable and efficient email delivery Delivery is often delayed because of back-and-forth processing between servers.
Helps to improve email security with features like message encryption and authentication. Configuration of SMTP server might be complex or require technical support
It improves email deliverability and scalability It limits to 7-bit ASCII characters only.
Universally adopted protocol

Comparing Email Protocols: SMTP vs. IMAP vs. POP3

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

Full Name Simple Mail Transfer Protocol Internet Messaging Access Protocol Post Office Protocol
Primary Use Sending emails Retrieving and managing emails Retrieving emails
Protocol Type Push protocol Pull protocol Pull protocol
Communication Scope Between email servers Between email client and server Between email client and server
Port Numbers 25 (default), 587 (encrypted) 143 (default), 993 (encrypted) 110 (default), 995 (encrypted)
Email Storage Organizes on client storage Manage emails on server Download to client and deletes from server
Access Method Single device access Multiple devices sync Single device access
Offline Access No Yes, with cached data Yes, after download
Email Status Sync No Yes No
Security Features TLS for encryption, SMTP-AUTH for authentication TLS for encryption SSL/TLS for encryption
Advantages Reliable delivery, support bulk emails Email sync across devices, access without download Offline access, simple implementation
Disadvantages No email retrieval, no status sync Require internet for full access, complex implementation No email sync; delete email from the server

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).

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