POP3

POP3, or Post Office Protocol 3, is a standard protocol used by email clients to retrieve emails from a mail server. It operates over TCP/IP and is commonly used for downloading emails to a local client. POP3 typically deletes the email from the server after download, although some configurations allow for emails to be left on the server.

What is POP3

POP3, or Post Office Protocol version 3, is a protocol used by email clients to retrieve emails from a mail server. It was designed to support offline email processing, meaning that emails are downloaded from the server to the client, and then typically deleted from the server. This allows users to access their emails even when they are not connected to the internet.

POP3 operates over TCP/IP and uses port 110 by default. It is a simple, text-based protocol that allows the client to connect to the server, retrieve messages, mark messages for deletion, and then disconnect. While it is a straightforward and widely supported protocol, it lacks some of the advanced features found in more modern email protocols like IMAP.

Despite its simplicity, POP3 has been a fundamental part of email communication for many years. It is supported by virtually all email clients and servers, making it a reliable choice for basic email retrieval. However, its limitations, such as the lack of synchronization between multiple devices, have led to a decline in its usage in favor of more feature-rich protocols.

POP3 runs on TCP and UDP port 110 and is official IANA port.

Security risk

If port 110 is open and the POP3 service is running, it can be a target for attackers looking to intercept email communications. Without proper encryption, sensitive information such as login credentials and email content can be exposed. Additionally, an open port can be exploited for unauthorized access to the email server.

In our UFW tutorial you can follow instructions how you can configure UFW to close port 110. Use StackChanges to monitor if the POP3 port is closed and stays closed. StackChanges will send an alert if port 110 is open again.