What function does POP serve in email communication?

POP, which stands for Post Office Protocol, is primarily utilized for retrieving emails from a mail server to a local client. When a user connects to their mail server using POP, the protocol allows the client to download messages from the server into the user's local mailbox. This means the user can read emails offline after they have been downloaded, as they are stored on the user's device rather than remaining on the server. POP effectively facilitates the reading and management of emails, which justifies why this function is accurately represented by option B.

In contrast, sending messages from a client to a mail server is typically handled by SMTP (Simple Mail Transfer Protocol), which is designed for sending emails rather than retrieving them. Storing messages on a web server is more characteristic of IMAP (Internet Message Access Protocol), which allows for managing and syncing messages across multiple devices. Finally, filtering spam messages is usually a function of email servers or specialized software, not a role played by POP in the email communication process.