Email Protocols Explained: SMTP vs POP3 vs IMAP

In this day and age, emails are an essential part of everyday communication. They connect companies with customers, marketers with their audiences, and people with one another.
Multiple components operate behind the scenes to make sure those communications are successful. These are email servers that receive messages from senders and transmit them to the recipients. For the transmission to be successful, mail servers have to establish connections with each other. That’s where email protocols come into play.

In today’s blog post, we’ll explain the main email protocols. We’ll put SMTP vs POP3 vs IMAP and highlight the major differences between them.

What is an email protocol?

An email protocol is a set of rules that makes it possible to send and receive emails. It defines standards that simplify the transmission of different email types between different mailbox providers and email clients. Thanks to email protocols, you can send emails from Yahoo! to Gmail or Outlook. And the recipient will be able to view your emails without any trouble.

We can compare email protocols to the standards of traditional mail. When you want to send a letter to your friend, you should write the address according to the established rules. Otherwise, your letter won’t be delivered to the correct address.

The same goes with email protocols – for your emails to be transmitted, they should satisfy the existing standards. This is true whether you’re sending promotional emails or transactional messages.

SMTP workflow

Simple Mail Transfer Protocol or SMTP is the only protocol used for sending emails. As you’ll see in our section about SMTP vs POP3 and IMAP, only one protocol deals with outgoing messages, while two protocols take care of incoming emails.

SMTP defines the rules that determine how an email gets from the sender to the email server.

(Source: Mailmodo)

An SMTP connection begins once you write your email and hit the send button. Your email client (a website or app you use to access your emails) will send a request to a mail server and let them know that it wants to establish a connection. Then the mail server has to verify the identity of the sender. If that’s successful, the server will agree to start the connection.

Once the connection is established, the client will slowly transmit all the data included in the email: body, attachments, date, from and to headers, subject lines, and even empty lines. When every component is transmitted, the client will request to terminate the connection.

The communication between the client and the server is conducted using text commands such as HELO, QUIT, DATA, etc.

Ports also participate in that process – these are endpoints that make it possible to identify the exact location of the address. Common ports used during SMTP connections are 25, 465, 587, and 2525. Out of these four, 587 and 2525 are considered to be more secure as they are usually used for TLS encryption.

SMTP is largely used for sending transactional or marketing messages. The latter applies to large corporations, tech startups, SaaS products, and other businesses. When you sit down to send an email to your colleague, you’ll also use the SMTP protocol.

Advantages of the SMTP protocol

The main advantage of the SMTP protocol is its simplicity. It’s easy to set up and use for sending messages. It doesn’t require complicated configurations and it’s usually the standard used by the majority of email service providers (ESPs).
Another benefit is that the SMTP server (the computer which operates using SMTP protocol) is easier to integrate with your website or app as it requires less coding.
Finally, SMTP logs errors when the messages aren’t sending, which simplifies the troubleshooting process.

Disadvantages of the SMTP protocol

The SMTP protocol is frequently criticized for having security vulnerabilities. For that reason, Enhanced Simple Transfer Protocol or ESMTP is often used instead.
SMTP protocol also has limitations in terms of functionalities. For example, it can’t be accessed offline and the data can’t be synced across multiple devices. Email transmission can also be slow because of the lengthy communication between the client and server.

POP3 workflow

POP3, short for Post Office Protocol 3, is an internet protocol used for retrieving emails from an email server. Currently, its third version is in use, hence the number 3 in its name.

(Source: MailBird)

Similar to SMTP, POP3 workflow begins when the client connects to the mail server. The connection is established through TCP port 110. The client authenticates itself by sending username and password information.

After successful authentication, all new messages stored on the server will be downloaded according to the rules determined by the POP3 protocol. When all the messages are retrieved, they get deleted from the server at the end of the session. This means that they won’t be accessible later on. We’ll talk more about that when we put POP vs IMAP below.

Pros of POP3 protocol

The main benefit of POP3 lies in the fact that users don’t need to do any configurations themselves. As a rule, email clients will activate the preferable option by default.
POP3 is also highly secure since the messages are downloaded directly from the server and deleted after the session ends. The protocol requires smaller resources, making it suitable for devices that have limited storage space.

Cons of POP3 protocol

As it’s usually the case, POP3 also has its downsides. When using this protocol, the server will download messages only when you log into your account. If you don’t use email frequently, received emails could clutter the server and slow down your connections.

Additionally, POP3 makes users dependent on the device. If you lose access to the device or something happens to it, you’ll also lose access to those emails. Likewise, it’s difficult to synchronize your actions across different devices. For example, if you delete emails from your laptop, they won’t be deleted from your phone if they were downloaded beforehand. That’s one of the main features we’ll notice while comparing email POP vs IMAP.

IMAP workflow

Internet Message Access Protocol (IMAP) is the protocol used for accessing emails on a remote mail server. It allows users to read and manage their messages remotely without downloading them onto their devices. This means that you can check your inbox from any place that has an internet connection.

(Source: Sloovi)

When someone sends an email to an IMAP account, the server will store it internally. The connection will begin when the recipient opens their email client and connects to the server through IMAP. The user will see all the headers in the inbox. When they click on a particular email, IMAP will download the full email on demand.

Pros of IMAP protocol

Email clients widely use IMAP due to its enhanced functionalities. The protocol supports two-way synchronization between multiple devices. This means that the changes you make will be reflected in other devices as well.

IMAP is also less dependent on devices – the messages are always stored on the server and will be accessible even if the device is no longer working.

IMAP supports push notifications, advanced search, automated replies or filters, as well as the ability to assign flags or labels. This gives users more control over their emails.

Cons of IMAP protocol

Since IMAP stores all emails on the server even after downloading them, it requires more storage space. Plus, the connection requires a network that can be unsecured at times. This can leave your emails and sensitive data stored in them vulnerable to third-party attacks.
Due to its complexity, IMAP is also harder to set up and manage if you decide to set it up manually. We’ll talk a bit more about it in our IMAP vs POP section.

How do these protocols differ?

Even though the concept of the email protocols is similar, there are still major differences between them. We’ll break down all the differences below by putting POP3 vs IMAP vs SMTP.

SMTP vs POP3 and IMAP

Unlike POP3 and IMAP, SMTP only deals with outgoing emails. Though it participates in different stages of the email journey, it’s not responsible for receiving messages. Both POP3 and IMAP store messages on their servers, while SMTP doesn’t. Think of it as a postal carrier who takes letters from the postal office to the recipient. In other words, SMTP is responsible for delivery, while POP3 and IMAP regulate how users access received messages.

These are the main differences we see when we put SMTP vs IMAP and POP3.

POP 3 vs IMAP

When it comes to POP email vs IMAP, the key differences are the following:

• IMAP stores emails on the server itself, while POP3 requires users to download messages locally;
• IMAP saves emails on the server even after you’ve read them, while POP3 deletes them at the end of the session;
• IMAP makes it possible to synchronize users’ actions on multiple devices, while POP3 doesn’t have that ability;
• Most email clients support IMAP by default, while POP3 may require manual configuration.

(Source: Mailtrim)

While comparing POP3 and IMAP, it’s important to mention that they are quite similar in terms of security. However, modern email clients still prefer IMAP as it gives more flexibility to the users.

All three of these protocols can be configured on a VPS server, cloud hosting, or dedicated servers.

Which protocols should I choose?

The answer depends on your goal. If you want to send large volumes of emails, you should opt for the SMTP protocol. As highlighted in the SMTP vs POP3 and IMAP section, SMTP will deliver your messages securely. It’s particularly suitable for businesses that rely on email marketing strategies and sends out thousands of messages to their subscribers.

If you want to access your inbox from multiple devices and you have limited storage space locally, then IMAP should be your choice. This protocol is also suitable for large corporations that receive masses of emails daily.

You should opt for POP3 if you don’t have an internet connection everywhere you go. You can download messages when your network is stable and access them later when you lose access to the internet.

Conclusion

This sums up our SMTP vs POP3 vs IMAP blog post. The choice between these protocols comes down to your goals. SMTP is the preferred protocol for sending bulk emails, while IMAP is the industry standard for receiving emails. POP3 is usually reserved for cases when you have limited resources.