SMTP vs POP3: Understanding How they Work

smtp vs pop3
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Email is an integral part of business communication and operations. From corporate firms to academic institutions, political, economic, and businesses, email is a widely accepted form of communication that is regarded as formal, confidential, and appropriate.

Email protocol predominantly determines how emails work from the sender to the receiver mail. It defines the mechanism of email exchange between email servers and clients, allowing users to send and receive emails correctly without error.

For every successful email communication, two mail agents – the messages transfer agent and message access agent are required to send and receive an email. While the message transfer agent transfers the message from the sender’s computer to the recipient’s email server, the message access agent receives the message from the recipient’s server to their computer.

There is one message transfer agent, which is the SMTP (Simple Mail Transfer Protocol), and two message access agents – POP (Post Office Protocol) and IMAP (Internet Message Access Protocol)

If you are wondering how email works with these three common protocols, this article has extensively explained the three protocols and the critical difference between SMTP vs. POP3, and the role of IMAP in layman’s terms.

Keep reading!

Table of Contents

  • What is an email protocol?
  • What is SMTP, POP3, and IMAP?
  • Benefits of Choosing POP3 over IMAP
  • How do sending and receiving emails work?
  • Key differences between SMTP and POP3
  • FAQs

What is an email protocol?

 pop3 vs smtp

An email protocol is a set of standard rules that makes sure that emails are transmitted properly over the internet, without any errors. Three common email protocols handle email transactions over the internet.

The three protocols – IMAP, POP3, and SMTP enable email users to access easily, send, receive and manage emails across various machines, networks, devices, email programs, and operating systems.

Different devices supporting the same protocol can effectively communicate, irrespective of the type of device or the manufacturer. In most cases, TCP/IP (Transmission Control Protocol/Internet Protocol) allows computers to communicate with one another over a long-distance network.

What is SMTP, POP3, and IMAP?

Your ability to send and receive emails daily is largely determinant of three key protocols – SMTP, IMAP, and POP3. In the section below, we have explained the protocols individually.

What is SMTP?

 imap vs pop3 vs smtp

Starting with the definition of SMTP being the only message transfer agent, SMTP is essentially used to handle outgoing emails.

Simple Mail Transfer Protocol (SMTP) is an email protocol used to send emails from a local mail client to the receiver mail server. It works with software called the message transfer agent (MTA) to transfer email messages to their correct destinations.

Aside from sending emails, a simple mail transfer protocol (SMTP) also acts as a shield to filter what messages pass through and the ones to be discarded. It also monitors and regulates the number of messages an account can send within a time frame.

SMTP servers are of two different types – relays and receivers. Relays accept the user’s emails and direct them to the recipient, while receivers receive the email from the relay servers and deliver them to the mailbox. Check out the detailed guide and know your email marketing mistakes.

Default SMTP Ports

SMTP uses the following ports:

  • Port 25 – is used to send messages in plain text, although many internet service providers block it as a security risk.
  • Port 587 – is registered by IANA as a secure SMTP port.
  • Port 465 – works over an implicit SSL connection

What is POP3?

 imap vs smtp vs pop3

POP3 which stands for Post Office Protocol version 3 is regarded as a one-way incoming mail protocol used to receive email messages from a mail server to a mail client.

POP3 downloads copies of email messages from an email server to a local machine, system, or email client. When the post office protocol completes downloading the copies, it deletes the original data from the server’s inbox, although many providers give the option to keep original copies intact.

The latest version of the post office protocol that is widely used is version 3, which brings about the name POP3. The POP3 essentially supports many authentication mechanisms and extensions important to prevent malicious or evil individuals from gaining unauthorized access to a user’s messages.

The main advantage of the post office protocol version 3 is that it allows users to read emails when offline and uses less of the email server’s storage.

However, a key disadvantage of POP3 is that works with one device and does not store email messages on the server, which can potentially lead to loss of emails when there’s no backup. Find the guide on how to create a personalized email.

Default POP3 Ports

POP3 uses the following ports:

  • Port 110 – is the default POP3 port and is unencrypted.
  • Port 995 – is the encrypted port for POP3 and works over TSL/SSL encryption.

What is IMAP?

 pop3 vs smtp vs imap

The Internet Message Access Protocol (IMAP) compared to POP3 is a two-way incoming email protocol that downloads only the email headers instead of the entire content.

Due to this, the email messages are retained on the server after the receiver views the email, making them easily accessible from other platforms. Its two-way communication enables it to sync every change made on the email client to the server.

This configuration is best for email users who want to access and interact with their email messages across multiple devices thereby eliminating the concerns of email loss should anything happen to the device which isn’t the case for POP3.

An additional benefit of using IMAP is that enables users to easily find a specific email message by using a keyword.

Default IMAP Ports

IMAP uses the following ports:

  • Port 143 – is the default IMAP port and is unencrypted
  • Port 993 – is the secure port for IMAP and works over TSL/SSL encryption

Benefits of Choosing POP3 over IMAP

 pop3 vs imap vs smtp

Here are some of the benefits of choosing POP3 over IMAP.

1. Email server storage space

Considering how important email storage space is for most users, one of the biggest advantages of choosing POP3 over IMAP is that it requires less storage space since it doesn’t leave messages on the server, unlike IMAP where consumer storage space is faster than POP3.

2. Computational overhead

IMAP offers more functionality of easy accessibility to mail messages, synchronization of messages, and organization, which consumers a lot more CPU and RAM with higher cost implications. A key benefit of using POP3 is that doesn’t use high CPU and memory storage which ultimately saves more cost and doesn’t require too many expenses to run.

3. Privacy

For most email users who constantly deal with confidential information, POP3 takes the weight off the major concerns of data or information breaches. Since POP3 doesn’t save email copies in the mail servers, users are allowed to download all email messages without leaving any copies behind on the mail server.

4. Security

The POP3 essentially supports many authentication mechanisms and extensions important to prevent malicious or evil individuals from gaining unauthorized access to a user’s messages. It provides security for email users and protects them from harm on the internet.

5. Speed

The speed of two incoming email protocols largely depends on the email requirement of the receiver. If an email user decides to download only the email headers or certain portions of the email such as the attachment alone, the IMAP can be regarded as faster in this.

However, if the email user decides to download all the messages on the server every single time, then the POP3 would be faster than IMAP.

How do sending and receiving emails work?

 smtp vs pop3 vs imap

Emails generally go through different stages from the receiver’s mail server to the sender’s mail server. An email message travels through at least two main SMTP servers for the senders and recipients.

Firstly, the SMTP protocol connects the email client with the email provider’s server by transferring the email messages from the sender’s device to the mail box present on the receiver’s mail server.

Next, it scans the email header for relevant information about the sender and the recipient’s address. Once it verifies the email destination, the email server will check the location with the address in the DNS (Doman Name System).

For example, if you are trying to send an email to, the server locates the email and relays the message to that particular email. After this, the recipient’s SMTP server delivers the message to the server’s mailbox until the intended user logs in to their email account.

After all this, the SMTP server sends the email to either of the POP3/IMAP servers, which will eventually forward the message to the email recipient’s email so they can access and interact with it.

Key differences between SMTP and POP3

 smtp vs imap vs pop3

1. Key difference

SMTP is a message transfer agent (MTA) that connects messages to the receiver mail server while the POP3 is a message access agent (MAA) that is used to access emails from the mailbox.

2. Full form

SMTP is referred to as a push protocol while POP3 is referred to as a pop protocol.

3. Number of times implied

The SMTP is implied twice, the first is between the sender and the sender mail server and the second time is between the sender mail server and the receiver mail server. While the POP3 is implied once between the receiver and the receiver’s mail server.


SMTP sends emails from the sender’s computer or device to the receiver’s mail server while the POP3 on the other hand retrieves and organizes emails from the receiver mail server to the receiver’s device.


There are three key TCP/IP protocols for delivering emails which include SMTP, POP3, and IMAP. While SMTP works predominantly to send emails, POP3 and IMAP are used to receive emails. Depending on what an email user wants to achieve – download only the email headers or access and download the entire email, they can choose between IMAP and POP3.

Frequently Asked Questions (FAQs).

1. What is STMP?

STMP which stands for Simple Mail Transfer Protocol is the standard protocol for sending email messages to email receivers.

2. What is POP3?

POP3 which stands for Post Office Protocol version 3 is the latest and most widely used incoming email protocol, that enables email users to receive emails and download them.

3. What is IMAP?

IMAP which stands for Internet Message Access Protocol is a popular protocol for receiving email messages that allow users to receive emails on more than one device.