What protocol uses TCP port 110?

The protocol that uses TCP port 110 is POP3, which stands for Post Office Protocol version 3. POP3 is a standard email protocol used for retrieving emails from a mail server. When a client (like an email application) connects to the mail server to fetch emails, it typically does so via TCP port 110.

One of the characteristics of POP3 is that it allows users to download mail from the server to their local devices, where they can read their emails offline. After emails are downloaded, the default behavior can be set to either delete them from the server or leave copies on the server, depending on the configuration.

Understanding the specific port assignments for various protocols helps in troubleshooting network issues and configuring firewalls appropriately to permit or deny access to certain services. In contrast, other protocols mentioned in the choices operate on different ports; for example, SMTP (Simple Mail Transfer Protocol) primarily uses TCP port 25, HTTP (Hypertext Transfer Protocol) uses TCP port 80, and HTTPS (HTTP Secure) operates on TCP port 443.