Written by Christian Ahmer | 11/20/2023


POP3 stands for Post Office Protocol version 3, which is the third version of a widespread protocol used to retrieve emails from a remote server to a local email client. POP3 is designed to be simple and robust, providing a user-friendly way to manage emails.

Here's an overview of how POP3 works:

  1. Connection: When the email client connects to the email server using POP3, it initiates a session over TCP/IP on port 110 by default, or port 995 for secure connections using SSL/TLS (known as POP3S).

  2. Authentication: The user must authenticate with a username and password to access their mailbox.

  3. Download: Once authenticated, the email client can download all the email messages from the server to the local device. POP3 traditionally does not leave messages on the server after download, although clients can be configured to leave messages on the server for a certain period.

  4. Deletion: Messages are marked for deletion on the server either after they have been downloaded or after the session ends. Some email clients allow users to leave copies of the messages on the server, which is useful if the user wants to access the same emails from multiple devices.

  5. Stateless: POP3 is generally a stateless protocol, meaning that once the client disconnects from the server, the server does not keep any state about the user's session. This is different from IMAP, which is stateful and allows for more advanced features like multiple folders and message status synchronization across devices.

  6. Limited Operations: With POP3, the email client can list the available messages, retrieve them, delete them, and nothing much beyond that. There are no provisions for flagging, searching, or managing folders on the server as there are with IMAP.

POP3 is suitable for users who access their email from a single device, such as a personal computer, and who want to maintain local copies of their emails. The simplicity of POP3 makes it less resource-intensive than more sophisticated protocols like IMAP.

However, the major limitation of POP3 is its lack of support for synchronization across multiple devices. Once the emails are downloaded to one device, they are typically removed from the server, making them inaccessible from other devices. This can be mitigated by configuring the email client to leave messages on the server, but it does not provide the same level of integration and synchronization that IMAP offers. Due to this, while POP3 is still in use, IMAP is often preferred for its more advanced features and flexibility.