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1Fix the driver behind crashes, sound loss and screen glitches2Repair Windows errors before they cause bigger problems3Scan for outdated or missing drivers - takes under a minuteIMAP (Internet Message Access Protocol) lets an email app access and manage messages stored in a mail server’s mailbox. Because the server holds the mailbox, your phone and computer can each synchronize a local view of it—including message status—rather than maintaining unrelated copies. IMAP does not send newly composed mail; a separate mail-submission protocol handles that.
What does IMAP mean?
IMAP stands for Internet Message Access Protocol. The current researched standard, IMAP4rev2, describes it this way: “The Internet Message Access Protocol Version 4rev2 (IMAP4rev2) allows a client to access and manipulate electronic mail messages on a server.” The IETF published RFC 9051 in August 2021: RFC 9051.
In practical terms, an email app is the client and the email provider’s system is the server. The server stores mail in mailboxes—often presented in an app as folders—and the client uses IMAP commands to inspect and manage those mailboxes remotely. A client can search messages, retrieve selected details or content, and change supported message flags without necessarily downloading every message body just to check mailbox state.
How does IMAP keep email in sync?
IMAP synchronization is a series of exchanges that lets an app reconcile its local view with the mailbox on the server. It is not necessarily a continuous, identical copy operation: clients decide what to cache and when to refresh, while the server remains the shared mailbox reference.
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- Connect and select a mailbox. The client connects to the server, authenticates, and selects the mailbox it needs to work with.
- Check mailbox state. The client can request mailbox status and message information, search messages, and fetch selected attributes or message content.
- Use local data when appropriate. An app may cache messages and status so it can display mail or support offline use. The exact storage and offline behavior depend on the app.
- Reconcile after a change or reconnect. The client compares its cached information with server state, refreshes what has changed, and can apply supported changes such as flag updates.
The protocol includes mechanisms for servers to report changes. RFC 9051 requires a server to send mailbox-size updates when it observes them while processing a command, and says it should automatically send observed flag updates. How quickly a particular app refreshes, whether it uses notifications, and what it downloads are implementation choices, not guarantees that all devices behave identically.
How does IMAP know which messages are which?
Message positions can change when mailbox contents change, so IMAP provides identifiers that help clients keep track across sessions.
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- Sequence number: A message’s current position in a selected mailbox. It is not a durable identity because that position can shift.
- UID: A server-assigned identifier intended to persist for a message within a mailbox’s UID validity context. Clients can use UIDs to match cached records to messages during later synchronization.
- UIDVALIDITY: A mailbox value that tells a client whether its previously cached UIDs remain valid. If UIDVALIDITY changes, the client must treat its old UID mapping for that mailbox as invalid and rebuild or reconcile its cache.
- UIDNEXT: The server’s predicted UID for a new message. It can help a client notice possible arrivals, but does not guarantee that a message will receive that exact UID.
These identifiers explain why a client may need to refresh or rebuild part of its local mailbox data rather than assuming that a message’s old position still identifies it.
What message changes can IMAP synchronize?
IMAP flags represent common message state. Standard system flags include Seen (seen/read), Answered, Flagged, Deleted, and Draft. A flag’s persistence depends on what the server advertises and permits: some flags can be permanent, while others may be session-only.
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Deleted deserves particular care. It marks a message for later removal; marking it deleted is not itself the same as permanently expunging it from the mailbox. An app’s delete behavior may involve additional steps, so the flag alone does not tell you exactly when a message disappears for good.
Does IMAP send email?
No. IMAP accesses and manages messages already in server mailboxes; it does not define how a newly composed message is submitted for delivery. RFC 9051 identifies mail submission as a separate function, with a protocol such as RFC 6409 as an example. Email apps often combine mailbox access and message submission behind one interface, which can make both functions seem like one protocol.
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Are all IMAP features the same across providers?
No. IMAP defines common mailbox operations, but providers can add extensions that work only with compatible servers and clients. Google, for example, documents Gmail-specific extensions for labels, special-use folders, and Gmail message and thread IDs. Its documentation says clients can discover these extensions through CAPABILITY; X-GM-EXT-1 signals support for the documented Gmail extensions. Those labels and X-GM-* attributes are Gmail-specific, not universal IMAP features: Gmail IMAP Extensions.
What IMAP does—and does not—guarantee
IMAP provides a standard way for a client to access and manage server-side mailboxes and reconcile mailbox information. It does not, by itself, promise a particular app’s offline storage, refresh schedule, notification method, account setup, or authentication experience. Those details depend on the email provider and client. RFC 9051 specifies IMAP4rev2; many deployed clients and servers also support IMAP4rev1 or extensions, so implementation details can vary. For synchronization guidance covering disconnected clients and cache reconciliation, see RFC 4549.
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