What is IMAP?
Also known as: Internet Message Access Protocol
IMAP is an email protocol that lets clients access and manage messages stored on a mail server, keeping the server as the authoritative copy and synchronizing folder state across multiple devices.
The Internet Message Access Protocol (IMAP) is an application-layer protocol used by email clients to retrieve and manage messages from a remote mail server. Unlike POP3, which downloads and often deletes messages from the server, IMAP keeps the messages on the server by design. This allows users to access their entire mailbox from multiple devices (desktop, phone, webmail) while seeing the same folder structure, read state, and flags.
IMAP operates over TCP, typically on port 143 for plaintext connections or port 993 for implicit TLS. The protocol works in a client-server model: the client opens a connection, authenticates (often with the LOGIN command or SASL mechanisms), and then issues commands such as SELECT INBOX, FETCH, STORE, SEARCH, and LOGOUT. The server responds with tagged status codes and data. IMAP supports concurrent access from multiple clients, and an extension called IDLE (RFC 2177) allows the server to push new message notifications to the client without polling.
IMAP is the backbone of modern email access for users who check mail on more than one device. It coexists with SMTP for sending, and POP3 remains an alternative for those who prefer offline access. The protocol has gone through several revisions, with IMAP4rev1 (RFC 3501) being the widely deployed version as of 2025. Its design centers on the idea that the mail store lives on the server, and the client is a transient viewer of that store.
Key facts
- Messages remain on the server by default; clients download copies for local caching.
- The protocol supports multiple folders, flags (seen, flagged, deleted), and server-side searches.
- Defined in RFC 3501 (IMAP4rev1), published in 2003.
- Operates over TCP port 143 (plain) or 993 (IMAPS, implicit TLS).
- Extensions like IDLE (RFC 2177) enable push notifications for new mail.
How it works in practice
Related terms
References
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