Which protocol does IMAP4 replace?

IMAP4, which stands for Internet Message Access Protocol version 4, is designed to enable users to access their email messages directly on the email server, allowing for more flexible and efficient management of email. It effectively replaces POP3, or Post Office Protocol version 3, which is an earlier standard used for retrieving emails.

While POP3 allows users to download emails to their device for offline access, it typically does not support advanced features such as organizing emails into folders, maintaining email states (like read or unread), and syncing between multiple devices. IMAP4, on the other hand, allows users to view their emails in real time and keeps messages synchronized across all devices. This capability makes it particularly useful for users who access their email from multiple devices, such as a smartphone, tablet, and computer.

The other protocols listed—SMTP (which is used for sending emails), HTTP (which is the protocol for transferring web pages), and FTP (used for transferring files)—serve different purposes and are not directly related to email retrieval in the same way that IMAP4 and POP3 are. This context highlights why IMAP4 specifically replaces POP3 rather than any of the other options.