IMAP and POP3 Protocols Email Client Communication

IMAP and POP3 Protocols Email Client Communication
Published in : 29 Dec 2023

IMAP and POP3 Protocols Email Client Communication

Emails are transmitted by email servers but also through specific email programs called email clients. These email clients, such as Mozilla Thunderbird or Windows Live Mail, use protocols to display emails.

The procedure differs depending on each protocol used: the IMAP network protocol opens messages directly on the server, while the POP3 communication protocol downloads the data and then opens it locally.

IMAP: what's behind the network protocol

The IMAP protocol, from the English Internet Message Access Protocol, is a network text file transmission protocol that allows access to emails located on a server. If you configure your account with IMAP, your email client establishes a connection to the server during each consultation. You can access the different folders and emails whose contents will be loaded from the server on request.

All messages and email folder structures may be saved on the server and, therefore, accessible until deleted. Consulting your emails can be done from anywhere, on different computers and email clients connected to the Internet, which allows you to find your folder structures, letters, and other data constantly updated.

The connection between the server and the IMAP client is made via the TCP/IP transmission protocol on port 143 (port 993 with a more secure connection). The client communicates with the server via text messages and does not require direct responses to specific commands. To be able to record the server's feedback during the rest of the process, the client expresses its commands via signaling, to which the mail server will respond. Response lines start with an asterisk if its content contains information.

If the response header includes a "plus" sign, it means that the server expects to receive additional information about the received command. This feedback informs us about the success (OK), failure (NO), or even syntax error (BAD) of the respective IMAP client commands.

How does the POP3 transmission protocol work?

The POP3 protocol, Post Office Protocol in English, allows the extraction of emails using a client. For this purpose, the client establishes communication with a mail reception server on which it is necessary to install POP3 server software. In this configuration, emails are downloaded and saved on the email client's computer. Following this extraction, the electronic messages are deleted from the email server, and the connection is interrupted.

You can then open and process the content of the downloaded emails locally without the client and server being connected. The time required for the extraction process varies depending on the volume of email content. A message can only be downloaded from a POP3 client.

POP3 clients use port 110 during the process of connecting to the mail server via TCP/IP. If the connection is encrypted, port 995 is used. If the server and client are linked, they communicate by commands. These POP3 commands consist of a four-character limit as well as one or more parameters. The server responds directly to each command with a positive (+OK) or negative (-ERR) status announcement, as well as any additional information.

The POP3 transmission process consists of three main steps. The first step involves user identification, during which the client, using a username and password, identifies the corresponding mail server. Secondly, the actual message-loading process begins.

If all the emails have been downloaded and the client and server have properly disconnected, the data is then deleted. If an interruption occurs during loading, all data is retained so that it can be downloaded again later.

Differences between IMAP and POP3

A comparison between the two protocols highlights the differences between IMAP and POP3, which are considered elementary. While IMAP clients establish continuous communication with the server, the connection of a POP3 client is only made at a time, i.e. only when loading data with the POP3 server. This is closely related to users' use of email software, which can be significantly different.

With POP3, downloaded emails are then deleted from the email server. With the IMAP network protocol, your emails remain intact on the email server unless you delete them manually. This is also the reason why several email clients can have access to the same data sets at the same time via the IMAP protocol. With POP3, access to an isolated client is limited because all received emails are always downloaded to a local computer.

IMAP for multiple clients, POP3 for a single client

Different possibilities for using the two protocols also result from the differences between IMAP and POP3 mentioned above. As POP3 is limited to a single client and emails are systematically extracted in full, the use of this communication protocol is ideal if you want to remove your emails on a single client and therefore a single computer.

In addition, once the emails have been downloaded, connection to the mail server is no longer necessary, and you can view and process your emails without an Internet connection.

If you want to access the same email addresses from different media and email clients, the IMAP protocol is the best choice. This choice is even more reasonable if you want to access your emails everywhere when you are on the move, thanks to mobile Internet connections. You can also download emails on a case-by-case basis to view them offline.

If no local version of the email has been downloaded beforehand, you will need an Internet connection to view it. Thanks to the email loading function, it is possible to arrange and manage folder structures via IMAP and also associate processing statuses with your emails or archive sent messages. However, due to its additional functions and the fact that emails remain intact on the mail server until deleted, the IMAP protocol is significantly more resource-intensive than its POP3 counterpart.

If you have to decide between IMAP or POP3, remember to consider both your email usage needs and your available computing resources.



Q: What is the difference between IMAP and POP3 protocols?

A: The primary distinction lies in how they handle emails. IMAP allows users to access and manage emails directly on the server, keeping them synchronized across multiple devices. POP3, on the other hand, downloads emails to a local device and removes them from the server.

Q: How does IMAP work?

A: IMAP (Internet Message Access Protocol) enables email clients to connect to a server and access emails remotely. The protocol operates over TCP port 143, with a more secure connection using port 993. IMAP clients communicate with the server through text messages, allowing users to view, organize, and maintain emails on the server.

Q: What is the purpose of the POP3 protocol?

A: POP3 (Post Office Protocol) is designed for downloading emails to a local device. The client connects to the mail server, retrieves emails, and typically removes them from the server. This allows users to access and manage their emails offline.

Q: Can multiple devices access the same set of emails with IMAP?

A: Yes, IMAP allows multiple devices to access the same set of emails stored on the server. Changes made on one device, such as marking an email as read, are reflected across all devices connected to the same IMAP account.

Q: How does the POP3 transmission process work?

A: The POP3 transmission process involves user identification, message loading, and data deletion. The client identifies the user by providing a username and password, downloads emails from the server, and, if the process is successful, the data is deleted from the server.

Q: Which protocol is suitable for a single-client setup?

A: POP3 is ideal for a single-client setup where emails are downloaded to a local computer, and the connection to the mail server is intermittent. It's suitable for users who want to manage emails on a single device and do not require constant synchronization across multiple devices.

Q: Why choose IMAP over POP3 for accessing emails on different devices?

A: IMAP is preferable when users need to access the same set of emails from different devices. It keeps emails synchronized across devices, making it convenient for users who switch between computers, tablets, and smartphones.

Q: Is there a resource difference between IMAP and POP3?

A: Yes, IMAP is more resource-intensive than POP3 due to its additional features. Since emails remain on the server until deleted manually, IMAP requires a constant internet connection for accessing and managing emails.

Q: Can I use both IMAP and POP3 for the same email account?

A: Yes, some email providers support both IMAP and POP3 for the same email account. However, it's essential to configure your email client correctly, taking into account the specific settings for each protocol.

Q: How can I decide between IMAP and POP3 for my email needs?

A: Consider your usage patterns and preferences. Choose IMAP if you want synchronized access to emails across devices, and choose POP3 if you prefer managing emails on a single device and value offline access.