IMAP (Internet Message Access Protocol) is a standard email protocol that stores email messages on a mail server and allows the user to view and manipulate them as if they were stored locally on their device's mail client. IMAP operates over port 143, where it maintains a continuous connection to the mail server, allowing users to organize, delete, or mark their email without having to download it first. This continuous connection enables real-time updates of the email status across multiple devices, making it ideal for users who need to access their mail from various locations and devices.