IMAP is a protocol used by email clients to access messages stored on a mail server. It keeps messages on the server so users can check the same inbox from multiple devices without losing sync. Because IMAP stores state on the server, actions like marking messages read or moving them between folders remain consistent everywhere. IMAP communicates using structured commands that let clients fetch just the parts of messages they need, improving performance.
It supports server-side search so clients do not have to download everything first. IMAP also works well for unreliable connections because clients can resume interrupted operations. It provides folder management features that allow users to organize mail directly on the server.
Unlike older systems, IMAP assumes that storage is cheap and syncing is essential. It remains widely supported across email providers and clients. IMAP is part of the foundation of modern, multi-device email workflows. IMAP operates alongside SMTP, which handles sending rather than receiving.