SMTP vs POP3 – What’s the Difference ? (Pros and Cons)

SMTP vs POP3 – What’s the Difference ? (Pros and Cons). In this post, we introduce SMTP and POP3 , then we compare both tools based on their nature and the task they were designed for.

All in all, Email is one of the world’s most important modes of communication today. It has become an integral part of everyone’s life. However, have you ever thought about how email works? What protocols do you use for sending and receiving messages?

The answer is SMTP and POP3. These are also called ‘Push and Pop’ protocols. They are message transfer agents and message access agents, respectively. You need them for sending and receiving messages.

Shall we proceed with SMTP vs POP3 – What’s the Difference ? (Pros and Cons). Well…but first let us know about email protocol.

What Is Email Protocol?

Above all, there is a must to follow certain rules when you send or receive an email. These rules are called email protocols that help to transmit emails between the sender and the recipient. Email protocols are of two types: inbound and outbound. SMTP is an outbound email protocol, while POP3 is an inbound protocol.

The inbound protocol helps you view an email in your inbox. On the other hand, the outbound protocol allows you to relay the message to the recipient.

Steps are: you send an email and it is delivered to the email client server with the help of SMTP. The email then reaches the recipient’s email inbox with the help of POP3.

Interestingly, SMTP helps you send emails, and POP3 helps you receive emails.

What Is SMTP?

Image Source: openclipart

SMTP, short for simple message transfer protocol, is a rule book used by email servers for sending and receiving emails over the Internet. An SMTP server is just a technology running the simple mail transfer protocol in the email delivery process, acting a bit like the postman. Like most servers, an SMTP server processes data for transmission to another server. But it has a specific purpose for processing data related to sending, receiving, and transmitting emails.

Subsequently, SMTP is a protocol that defines a rule set for digital communications. However, the SMTP server is an application that handles the processes of email sending, receiving, and relaying. While SMTP is an email sending protocol, POP3 is a protocol for receiving emails. In other words, SMTP is used for sending emails from the sender to the receiver, whereas POP3 is used for receiving emails.

Also, SMTP is the push protocol for sending messages. You use POP3 (Post Office Protocol version 3) to deliver these messages on the receiving end. However, remember that you can only use SMTP servers to send your regular emails. For instance, those associated with providers such as Gmail, Hotmail, and Yahoo Mail. Here, you share users’ emails based on non dedicated IP addresses. 

Surely, the SMTP client uses commands to tell the SMTP server what to do and how to transmit data, such as the mail address of the sender, the recipient, and the contents of an email. A simple mail transfer protocol server is the communications protocol, or the technology, that underlies the exchange of emails.

Key Features of SMTP

When someone emails you, it is sent across the Internet, from one server to the next, using SMTP. Message transfer agents and other mail servers use SMTP to send and receive email messages.

Simple mail transfer protocol includes transferring mail from one server to another, provided the mail meets specific criteria. What differentiates SMTP from the other two protocols is that SMTP is the only protocol that sends, or pushes emails from one unknown email server to another.

The usual way of sending email over the internet is direct from a sender’s SMTP server to the receiver, using DNS MX records to identify the recipient’s SMTP server address.

When you click send on an email, the email client opens an SMTP connection with an SMTP server so that you send the message. Using this protocol, when you send the email, it will first open a TCP connection to an SMTP server, then send the email over a TCP connection.

Once it relays the signal for the TCP connection of any client, the TCP connection is initiated at port 25. When it is successfully connected, you immediately send out the email/message.

SMTP Features at a Glance

  • Uses port number 25.
  • SMTP is an inbound protocol.
  • It is a stateless protocol.
  • SMTP uses TCP at the connection layer so that it can send several emails at one go.
  • It is a connection driven protocol.

Pros of SMTP

  • In case of an email delivery failure, you will get a notification stating the reason for the failure.
  • SMTP only requires your credentials to work.
  • In the case of SMTP, it is very easy to use your mail for transactions. It is different in API, where you require coding.

Cons of SMTP

  • The security features of SMTP are not very strong.
  • Firewalls can easily block ports that you use with SMTP.
  • The simplicity of SMTP is also its biggest limitation.
  • SMTP is limited to only 7-bit ASCII characters.

Up next with SMTP vs POP3 – What’s the Difference ? we introduce POP3.

What Is POP3?

Image Source: openclipart

Next tool on the list is POP3. Also familiar as Post Office Protocol version 3, is the normal mail protocol for receiving emails to a local email client from a remote server. The recipient or their email client may regularly download the email from a server using the POP3.

When the email client checks the server using the POP3 protocol, it downloads the new messages, then removes them from the server. When the client wants to use POP3 to retrieve emails, it sets up a TCP connection with the server’s host. Each POP 3 email server has a different address, which needs to be inputted into an email program in order for it to connect to the protocol.

Post Office Protocol 3 is not intended to support email influence or integration in an email server. The emails are intended to be downloaded to a client and then erased by the server. Unlike current protocols, which utilize shared synchronization, POP3 only supports one way email synchronization. Allowing users to only download emails from a server to the client.

Key Features of POP3

When you use POP3 for checking email, an email client hooks the POP3 server and downloads email messages to the local machine. In the case of the POP3 protocol, you install a POP3 client in a recipient’s system and install the POP3 server on a recipient’s email server. The recipient, or the mail client, may download the mail from the server on a recurring basis using the POP3 protocol.

If you want to use POP3 to retrieve emails, it creates a TCP connection with the server’s host. It is the protocol an email client may use for downloading emails from the email server. Each POP3 email server has a separate address, which you need to type in your email program to connect to the protocol.

As we have mentioned earlier, Post Office Protocol 3 is not designed to support email synchronization in an email server. It needs to download the emails to a client and then erase it from the server.

POP3 Features at a Glance

  • It uses port number 110.
  • The protocol is an in band protocol.
  • It is a stateless protocol till such time you download the email and the stateless across the sessions.
  • POP3 is a connection driven protocol.

Pros of POP3

  • The process of configuring POP3 is simple.
  • One of the biggest merits of POP3 is that it allows the email to get downloaded on the recipient’s system. Thus, allowing you to view your emails even when you do not have an active internet connection.
  • POP3 allows you to open attachments in a simple way as you save them on the device.
  • There is less server space consumption with POP3 since you store all the emails on the local device.

Cons of POP3

  • You cannot access your emails from multiple systems.
  • There is a chance that your email folder can become corrupted, thus losing the entire mailbox in one go.
  • Email attachments that you receive may be virus infected. This could lead to harmful exposure to your device.
  • It isn’t easy to export the local mail folder to a different physical device or another mail client.

We came to the main article part of this blog post about SMTP vs POP3 – What’s the Difference ? 

SMTP vs POP3 - Key Differences

Both, SMTP and POP3 are email messaging protocols required to send and receive messages from email servers. With SMTP, you send, relaying, or forward messages from your email client, such as Gmail, to a receiving mail server.

User level client side mail applications use SMTP to send mail to the mail server, where it is transmitted. Well, SMTP passes messages from a client’s computer to a recipient’s mail server, whereas you use POP3 for receiving emails from an inbox. Moreover, SMTP defines the commands and responses to transmit messages between the client and the server MTA.



On one hand, the SMTP protocol stands for Simple Mail Transfer Protocol. Part of the application layer protocol and used to store and forward email.
In nutshell, SMTP transfers emails from the sender’s device to the mailbox of the recipient’s server. Also you may call SMTP a push protocol.


On the other hand, POP3 stands for Post Office Protocol. Used for receiving email from email server. POP3 retrieves the emails from the recipient’s server to their device. You can also call POP3 a pull protocol.



Designed for sending emails. It is also called a Message Transfer Agent (MTAs). The protocol has two MTAs. One is server message transfer agent and second is client message transfer agent.


Used for receiving email from remote servers to local mail box. It is also called a Message Access Agent. The protocol has two MAAs. One is server message access agent and second is client message access agent.

Implementation and Ports


The SMTP uses ports 25, 465, and 587 for sending emails. Port 25 is a standard SMTP port, 465 is a out of date secure port and 587 is a modern port for secure SMTP.


The POP3 uses ports 110 or 995 for receiving emails. Port 110 is the default port and does not provide encryption. On the other hand the port 995 is secure port and provide encryption.



The SMTP protocol acts as a MTA (Message Transfer Agent) for sending the message to the receiver. SMTP is still the Internet’s standard email protocol. But Internet hosts use a wide range of operating systems, and people can read and send mail using any user agent (UA) capable of communicating with an MTA.


The POP3 is a MAA (Message Access Agent) for accessing the messages from mail box. This protocol is programmed for users to download emails while connected to an email server (via Ethernet, Internet, or a VPN network connection). A POP3 connection allows for quick and easy email downloads on a personal PC.

Target Usage


The SMTP takes mail from the mail user agent (MUA) and makes sure the same gets delivered on a designated address mentioned on an email. SMTP is used for receiving and sending emails (like your letter carrier picking up and dropping off your mail at various locations)


Lastly, POP3 allows for the collection of email messages from a server and helps to load them to a designated address. POP3 is a protocol used to store emails (like your own post office box to store mail).

Thank you for reading SMTP vs POP3 – What’s the Difference ? (Pros and Cons). We shall conclude now.

SMTP vs POP3 - What's the Difference ? (Pros and Cons) Conclusion

Summing up, SMTP and POP3 are a pair of the most extensively used email protocols worldwide. By now, you must have understood the functions and features of both protocols in detail. When you send an email, it is delivered to the email-client server with the help of SMTP. The email then reaches the recipient’s email inbox with the help of POP3.

Undeniably, SMTP is one of the most universally used email protocols, alongside protocols such as IMAP and POP. Most well known email clients, like Gmail, Yahoo Mail, Outlook, and Apple Mail, support SMTP email protocols for sending messages.

To read more about email protocols, please navigate to our section called email over here.

Avatar for Hitesh Jethva
Hitesh Jethva

I am a fan of open source technology and have more than 10 years of experience working with Linux and Open Source technologies. I am one of the Linux technical writers for Cloud Infrastructure Services.

0 0 votes
Article Rating
Notify of
Inline Feedbacks
View all comments
Would love your thoughts, please comment.x