RFC 1730 (rfc1730) - Page 1 of 73
Internet Message Access Protocol - Version 4
Alternative Format: Original Text Document
Network Working Group M. Crispin
Request for Comments: 1730 University of Washington
Category: Standards Track December 1994
INTERNET MESSAGE ACCESS PROTOCOL - VERSION 4
Status of this Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Abstract
The Internet Message Access Protocol, Version 4 (IMAP4) allows a
client to access and manipulate electronic mail messages on a server.
IMAP4 permits manipulation of remote message folders, called
"mailboxes", in a way that is functionally equivalent to local
mailboxes. IMAP4 also provides the capability for an offline client
to resynchronize with the server (see also [IMAP-DISC]).
IMAP4 includes operations for creating, deleting, and renaming
mailboxes; checking for new messages; permanently removing messages;
setting and clearing flags; RFC 822 and MIME parsing; searching; and
selective fetching of message attributes, texts, and portions
thereof. Messages in IMAP4 are accessed by the use of numbers.
These numbers are either message sequence numbers (relative position
from 1 to the number of messages in the mailbox) or unique
identifiers (immutable, strictly ascending values assigned to each
message, but which are not necessarily contiguous).
IMAP4 supports a single server. A mechanism for supporting multiple
IMAP4 servers is discussed in [IMSP].
IMAP4 does not specify a means of posting mail; this function is
handled by a mail transfer protocol such as [SMTP].
IMAP4 is designed to be upwards compatible from the [IMAP2] protocol.
Compatibility issues are discussed in [IMAP-COMPAT].
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RFC 1730 IMAP4 December 1994
Table of Contents
IMAP4 Protocol Specification ...................................... 1
1. Organization of this Document ............................. 1
1.1. How to Read This Document ................................. 1
1.2. Conventions Used in this Document ......................... 1
2. Protocol Overview ......................................... 1
2.1. Link Level ................................................ 1
2.2. Commands and Responses .................................... 1
2.2.1. Client Protocol Sender and Server Protocol Receiver ....... 2
2.2.2. Server Protocol Sender and Client Protocol Receiver ....... 2
3. State and Flow Diagram .................................... 4
3.1. Non-Authenticated State ................................... 4
3.2. Authenticated State ....................................... 4
3.3. Selected State ............................................ 4
3.4. Logout State .............................................. 4
4. Data Formats .............................................. 6
4.1. Atom ...................................................... 6
4.2. Number .................................................... 6
4.3. String .................................................... 6
4.3.1. 8-bit and Binary Strings .................................. 7
4.4. Parenthesized List ........................................ 7
4.5. NIL ....................................................... 7
5. Operational Considerations ................................ 8
5.1. Mailbox Naming ............................................ 8
5.2. Mailbox Size and Message Status Updates ................... 8
5.3. Response when no Command in Progress ...................... 8
5.4. Autologout Timer .......................................... 9
5.5. Multiple Commands in Progress ............................. 9
6. Client Commands ........................................... 10
6.1. Client Commands - Any State ............................... 10
6.1.1. CAPABILITY Command ........................................ 10
6.1.2. NOOP Command .............................................. 11
6.1.3. LOGOUT Command ............................................ 11
6.2. Client Commands - Non-Authenticated State ................. 12
6.2.1. AUTHENTICATE Command ...................................... 12
6.2.2. LOGIN Command ............................................. 14
6.3. Client Commands - Authenticated State ..................... 14
6.3.1. SELECT Command ............................................ 15
6.3.2. EXAMINE Command ........................................... 16
6.3.3. CREATE Command ............................................ 17
6.3.4. DELETE Command ............................................ 18
6.3.5. RENAME Command ............................................ 18
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RFC 1730 IMAP4 December 1994
6.3.6. SUBSCRIBE Command ......................................... 19
6.3.7. UNSUBSCRIBE Command ....................................... 19
6.3.8. LIST Command .............................................. 20
6.3.9. LSUB Command .............................................. 22
6.3.10. APPEND Command ............................................ 22
6.4. Client Commands - Selected State .......................... 23
6.4.1. CHECK Command ............................................. 23
6.4.2. CLOSE Command ............................................. 24
6.4.3. EXPUNGE Command ........................................... 25
6.4.4. SEARCH Command ............................................ 25
6.4.5. FETCH Command ............................................. 29
6.4.6. PARTIAL Command ........................................... 32
6.4.7. STORE Command ............................................. 33
6.4.8. COPY Command .............................................. 34
6.4.9. UID Command ............................................... 35
6.5. Client Commands - Experimental/Expansion .................. 37
6.5.1. X Command ........................................... 37
7. Server Responses .......................................... 38
7.1. Server Responses - Status Responses ....................... 39
7.1.1. OK Response ............................................... 40
7.1.2. NO Response ............................................... 40
7.1.3. BAD Response .............................................. 41
7.1.4. PREAUTH Response .......................................... 41
7.1.5. BYE Response .............................................. 41
7.2. Server Responses - Server and Mailbox Status .............. 42
7.2.1. CAPABILITY Response ....................................... 42
7.2.2. LIST Response ............................................. 43
7.2.3. LSUB Response ............................................. 44
7.2.4. SEARCH Response ........................................... 44
7.2.5. FLAGS Response ............................................ 44
7.3. Server Responses - Message Status ......................... 45
7.3.1. EXISTS Response ........................................... 45
7.3.2. RECENT Response ........................................... 45
7.3.3. EXPUNGE Response .......................................... 45
7.3.4. FETCH Response ............................................ 46
7.3.5. Obsolete Responses ........................................ 51
7.4. Server Responses - Command Continuation Request ........... 51
8. Sample IMAP4 session ...................................... 52
9. Formal Syntax ............................................. 53
10. Author's Note ............................................. 64
11. Security Considerations ................................... 64
12. Author's Address .......................................... 64
Appendices ........................................................ 65
A. Obsolete Commands ......................................... 65
A.6.3.OBS.1. FIND ALL.MAILBOXES Command ........................ 65
A.6.3.OBS.2. FIND MAILBOXES Command ............................ 65
A.6.3.OBS.3. SUBSCRIBE MAILBOX Command ......................... 66
A.6.3.OBS.4. UNSUBSCRIBE MAILBOX Command ....................... 66
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RFC 1730 IMAP4 December 1994
B. Obsolete Responses ........................................ 68
B.7.2.OBS.1. MAILBOX Response .................................. 68
B.7.3.OBS.1. COPY Response ..................................... 68
B.7.3.OBS.2. STORE Response .................................... 69
C. References ................................................ 70
E. IMAP4 Keyword Index ....................................... 71
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RFC 1730 IMAP4 December 1994
IMAP4 Protocol Specification
1. Organization of this Document
1.1. How to Read This Document
This document is written from the point of view of the implementor of
an IMAP4 client or server. Beyond the protocol overview in section
2, it is not optimized for someone trying to understand the operation
of the protocol. The material in sections 3 through 5 provides the
general context and definitions with which IMAP4 operates.
Sections 6, 7, and 9 describe the IMAP commands, responses, and
syntax, respectively. The relationships among these are such that it
is almost impossible to understand any of them separately. In
particular, one should not attempt to deduce command syntax from the
command section alone; one should instead refer to the formal syntax
section.
1.2. Conventions Used in this Document
In examples, "C:" and "S:" indicate lines sent by the client and
server respectively.
2. Protocol Overview
2.1. Link Level
The IMAP4 protocol assumes a reliable data stream such as provided by
TCP. When TCP is used, an IMAP4 server listens on port 143.
2.2. Commands and Responses
An IMAP4 session consists of the establishment of a client/server
connection, an initial greeting from the server, and client/server
interactions. These client/server interactions consist of a client
command, server data, and a server completion result response.
All interactions transmitted by client and server are in the form of
lines; that is, strings that end with a CRLF. The protocol receiver
of an IMAP4 client or server is either reading a line, or is reading
a sequence of octets with a known count followed by a line.
Crispin
