Network Working Group A. Gulbrandsen
Request for Comments: 5465 Oryx Mail Systems GmbH
Updates: 5267 C. King
Category: Standards Track A. Melnikov
Isode Ltd.
February 2009
The IMAP NOTIFY Extension
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.
Copyright Notice
Copyright (c) 2009 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (http://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document.
Abstract
This document defines an IMAP extension that allows a client to
request specific kinds of unsolicited notifications for specified
mailboxes, such as messages being added to or deleted from such
mailboxes.
Table of Contents
1. Overview and Rationale ..........................................3
2. Conventions Used in This Document ...............................4
3. The NOTIFY Extension ............................................4
3.1. The NOTIFY Command .........................................4
4. Interaction with the IDLE Command ...............................8
5. Event Types .....................................................8
5.1. FlagChange and AnnotationChange ............................9
5.2. MessageNew .................................................9
5.3. MessageExpunge ............................................10
5.4. MailboxName ...............................................11
5.5. SubscriptionChange ........................................12
5.6. MailboxMetadataChange .....................................12
5.7. ServerMetadataChange ......................................13
5.8. Notification Overflow .....................................13
5.9. ACL (Access Control List) Changes .........................13
6. Mailbox Specification ..........................................14
6.1. Mailbox Specifiers Affecting the Currently
Selected Mailbox ..........................................14
6.2. Personal ..................................................15
6.3. Inboxes ...................................................15
6.4. Subscribed ................................................15
6.5. Subtree ...................................................15
6.6. Mailboxes .................................................16
7. Extension to SEARCH and SORT Commands ..........................16
8. Formal Syntax ..................................................16
9. Security Considerations ........................................19
10. IANA Considerations ...........................................19
10.1. Initial LIST-EXTENDED Extended Data Item Registrations ...19
11. Acknowledgements ..............................................20
12. Normative References ..........................................20
13. Informative References ........................................21
1. Overview and Rationale
The IDLE command (defined in [RFC2177]) provides a way for the client
to go into a mode where the IMAP server pushes it notifications about
IMAP mailstore events for the selected mailbox. However, the IDLE
extension doesn't restrict or control which server events can be
sent, or what information the server sends in response to each event.
Also, IDLE only applies to the selected mailbox, thus requiring an
additional TCP connection per mailbox.
This document defines an IMAP extension that allows clients to
express their preferences about unsolicited events generated by the
server. The extension allows clients to only receive events that
they are interested in, while servers know that they don't need to go
to the effort of generating certain types of untagged responses.
Without the NOTIFY command defined in this document, an IMAP server
will only send information about mailstore changes to the client in
the following cases:
- as the result of a client command (e.g., FETCH responses to a
FETCH or STORE command),
- as unsolicited responses sent just before the end of a command
(e.g., EXISTS or EXPUNGE) as the result of changes in other
sessions, and
- during an IDLE command.
The NOTIFY command extends what information may be returned in those
last two cases, and also permits and requires the server to send
information about updates between commands. The NOTIFY command also
allows for the client to extend what information is sent unsolicited
about the selected mailbox and to request some update information to
be sent regarding other mailboxes.
The interaction between IDLE and NOTIFY commands is described in
Section 4.
For the new messages delivered to or appended to the selected
mailbox, the NOTIFY command can be used to request that a set of
attributes be sent to the client in an unsolicited FETCH response.
This allows a client to be a passive recipient of events and new mail
and to be able to maintain full synchronisation without having to
issue any subsequent commands except to modify the state of the
mailbox on the server.
Some mobile clients, however, may want mail "pushed" only for mail
that matches a SEARCH pattern. To meet that need, [RFC5267] is
augmented by this document to extend the UPDATE return option to
specify a list of fetch-atts to be returned when a new message is
delivered or appended in another session.
2. Conventions Used in This Document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
The acronym MSN stands for Message Sequence Numbers (see Section
2.3.1.2 of [RFC3501]).
Example lines prefaced by "C:" are sent by the client and ones
prefaced by "S:", by the server. "[...]" means elision.
3. The NOTIFY Extension
IMAP servers that support this extension advertise the NOTIFY
capability. This extension adds the NOTIFY command as defined in
Section 3.1.
EID 3824 (Verified) is as follows:Section: 3
Original Text:
IMAP servers that support this extension advertise the NOTIFY
capability. This extension adds the NOTIFY command as defined in
Section 5.1.
Corrected Text:
IMAP servers that support this extension advertise the NOTIFY
capability. This extension adds the NOTIFY command as defined in
Section 3.1.
Notes:
Wrong section reference.
A server implementing this extension is not required to implement
LIST-EXTENDED [RFC5258], even though a NOTIFY-compliant server must
be able to return extended LIST responses, defined in [RFC5258].
3.1. The NOTIFY Command
EID 1804 (Verified) is as follows:Section: 3.1
Original Text:
page 7
C: b notify set status (selected MessageNew (uid
body.peek[header.fields (from to subject)]) MessageExpunge)
(subtree Lists MessageNew)
Page 8
C: e notify set (selected MessageNew (uid
body.peek[header.fields (from to subject)]) MessageExpunge)
(subtree Lists MessageNew) (mailboxes misc MessageNew)
Corrected Text:
page 7
C: b notify set status (selected (MessageNew (uid
body.peek[header.fields (from to subject)]) MessageExpunge))
(subtree Lists (MessageNew))
Page 8
C: e notify set (selected (MessageNew (uid
body.peek[header.fields (from to subject)]) MessageExpunge))
(subtree Lists (MessageNew)) (mailboxes misc (MessageNew))
Notes:
Incorrect syntax in example... each "events" set needs to be in parentheses.
Arguments: "SET"
Optional STATUS indicator
Mailboxes to be watched
Events about which to notify the client
Or
Arguments: "NONE"
Responses: Possibly untagged STATUS responses (for SET)
Result: OK - The server will notify the client as requested.
NO - Unsupported NOTIFY event, NOTIFY too complex or
expensive, etc.
BAD - Command unknown, invalid, unsupported, or has
unknown arguments.
The NOTIFY command informs the server that the client listens for
event notifications all the time (even when no command is in
progress), and requests the server to notify it about the specified
set of events. The NOTIFY command has two forms. NOTIFY NONE
specifies that the client is not interested in any kind of event
happening on the server. NOTIFY SET replaces the current list of
interesting events with a new list of events.
Until the NOTIFY command is used for the first time, the server only
sends notifications while a command is being processed, and notifies
the client about these events on the selected mailbox (see Section 5
for definitions): MessageNew, MessageExpunge, or FlagChange. It does
not notify the client about any events on other mailboxes.
The effect of a successful NOTIFY command lasts until the next NOTIFY
command or until the IMAP connection is closed.
A successful NOTIFY SET command MUST cause the server to immediately
return any accumulated changes to the currently selected mailbox (if
any), such as flag changes and new or expunged messages. Thus, a
successful NOTIFY SET command implies an implicit NOOP command.
The NOTIFY SET command can request notifications of message-related
changes to the selected mailbox, whatever that may be at the time the
message notifications are being generated. This is done by
specifying either the SELECTED or the SELECTED-DELAYED mailbox
selector (see Section 6.1) in the NOTIFY SET command. If the
SELECTED/SELECTED-DELAYED mailbox selector is not specified in the
NOTIFY SET command, this means that the client doesn't want to
receive any <message-event>s for the currently selected mailbox.
This is the same as specifying SELECTED NONE.
The client can also request notifications on other mailboxes by name
or by a limited mailbox pattern match. Message-related notifications
returned for the currently selected mailbox will be those specified
by the SELECTED/SELECTED-DELAYED mailbox specifier, even if the
selected mailbox also appears by name (or matches a pattern) in the
command. Non-message-related notifications are controlled by mailbox
specifiers other than SELECTED/SELECTED-DELAYED.
If the NOTIFY command enables MessageNew, MessageExpunge,
AnnotationChange, or FlagChange notifications for a mailbox other
than the currently selected mailbox, and the client has specified the
STATUS indicator parameter, then the server MUST send a STATUS
response for that mailbox before NOTIFY's tagged OK. If MessageNew
is enabled, the STATUS response MUST contain MESSAGES, UIDNEXT, and
UIDVALIDITY. If MessageExpunge is enabled, the STATUS response MUST
contain MESSAGES. If either AnnotationChange or FlagChange are
included and the server also supports the CONDSTORE [RFC4551] and/or
QRESYNC [RFC5162] extensions, the STATUS response MUST contain
UIDVALIDITY and HIGHESTMODSEQ. Absence of the STATUS indicator
parameter allows the client to avoid the additional STATUS responses.
This might be useful if the client already retrieved this information
before issuing the NOTIFY command.
Clients are advised to limit the number of mailboxes used with
NOTIFY. Particularly, if a client asks for events for all accessible
mailboxes, the server may swamp the client with updates about shared
mailboxes. This may reduce the client's battery life. Also, this
wastes both server and network resources.
For each mailbox specified, the server verifies that the client has
access using the following test:
- If the name does not refer to an existing mailbox, the server MUST
ignore it.
- If the name refers to a mailbox that the client can't LIST, the
server MUST ignore it. For a server that implements [RFC4314],
this means that if the client doesn't have the 'l' (lookup) right
for the name, then the server MUST ignore the mailbox. This
behavior prevents disclosure of potentially confidential
information to clients who don't have rights to know it.
- If the name refers to a mailbox that the client can LIST (e.g., it
has the 'l' right from [RFC4314]), but the client doesn't have
another right required for processing of the specified event(s),
then the server MUST respond with an untagged extended LIST
response containing the \NoAccess name attribute.
The server SHOULD return the tagged OK response if the client has
access to at least one of the mailboxes specified in the current list
of interesting events. The server MAY return the tagged NO response
if the client has no access to any of the specified mailboxes and no
access can ever be granted in the future (e.g., the client specified
an event for 'Subtree Bar/Foo', 'Bar/Foo' doesn't exist, and LIST
returns \Noinferiors for the parent 'Bar').
If the notification would be prohibitively expensive for the server
(e.g., "notify me of all flag changes in all mailboxes"), the server
MAY refuse the command with a tagged NO [NOTIFICATIONOVERFLOW]
response.
If the client requests information for events of an unsupported type,
the server MUST refuse the command with a tagged NO response (not a
BAD). This response SHOULD contain the BADEVENT response code, which
MUST list names of all events supported by the server.
Here's an example:
S: * OK [CAPABILITY IMAP4REV1 NOTIFY]
C: a login bob alice
S: a OK Password matched
C: b notify set status (selected MessageNew (uid
body.peek[header.fields (from to subject)]) MessageExpunge)
(subtree Lists MessageNew)
S: * STATUS Lists/Lemonade (UIDVALIDITY 4 UIDNEXT 9999 MESSAGES
500)
S: [...]
S: * STATUS Lists/Im2000 (UIDVALIDITY 901 UIDNEXT 1 MESSAGES 0)
S: b OK done
C: c select inbox
S: [...] (the usual 7-8 responses to SELECT)
S: c OK INBOX selected
(Time passes. A new message is delivered to mailbox
Lists/Lemonade.)
S: * STATUS Lists/Lemonade (UIDVALIDITY 4 UIDNEXT 10000
MESSAGES 501)
(Time passes. A new message is delivered to inbox.)
S: * 127 FETCH (UID 127001 BODY[HEADER.FIELDS (From To
Subject)] {75}
S: Subject: Re: good morning
S: From: alice@example.org
S: To: bob@example.org
S:
S: )
(Time passes. The client decides it wants to know about
one more mailbox. As the client already knows necessary
STATUS information for all mailboxes below the Lists
mailbox, and because "notify set status" would cause
STATUS responses for *all* mailboxes specified in the
NOTIFY command, including the ones for which the client
already knows STATUS information, the client issues a
NOTIFY SET without the STATUS parameter, followed by an
explicit STATUS request for the newly-added mailbox.
Note that if these two commands were issued in the reverse
order, that would be a client bug; changes may occur in
the mailbox between the completion of the STATUS command,
and the issuing of the NOTIFY command. The client may
never be notified of such changes.)
C: d notify set (selected MessageNew (uid
body.peek[header.fields (from to subject)]) MessageExpunge)
(subtree Lists MessageNew) (mailboxes misc MessageNew)
S: d OK done
C: e STATUS misc (UIDVALIDITY UIDNEXT MESSAGES)
S: * STATUS misc (UIDVALIDITY 1 UIDNEXT 999)
S: e STATUS completed
EID 2318 (Verified) is as follows:Section: 3.1
Original Text:
(Time passes. The client decides it wants to know about
one more mailbox. As the client already knows necessary
STATUS information for all mailboxes below the Lists
mailbox, and because "notify set status" would cause
STATUS responses for *all* mailboxes specified in the
NOTIFY command, including the ones for which the client
already knows STATUS information, the client issues an
explicit STATUS request for the mailbox to be added to
the watch list, followed by the NOTIFY SET without the
STATUS parameter.)
C: d STATUS misc (UIDVALIDITY UIDNEXT MESSAGES)
S: * STATUS misc (UIDVALIDITY 1 UIDNEXT 999)
S: d STATUS completed
C: e notify set (selected MessageNew (uid
body.peek[header.fields (from to subject)]) MessageExpunge)
(subtree Lists MessageNew) (mailboxes misc MessageNew)
S: e OK done
Corrected Text:
(Time passes. The client decides it wants to know about
one more mailbox. As the client already knows necessary
STATUS information for all mailboxes below the Lists
mailbox, and because "notify set status" would cause
STATUS responses for *all* mailboxes specified in the
NOTIFY command, including the ones for which the client
already knows STATUS information, the client issues a
NOTIFY SET without the STATUS parameter, followed by an
explicit STATUS request for the newly-added mailbox.
Note that if these two commands were issued in the reverse
order, that would be a client bug; changes may occur in
the mailbox between the completion of the STATUS command,
and the issuing of the NOTIFY command. The client may
never be notified of such changes.)
C: d notify set (selected MessageNew (uid
body.peek[header.fields (from to subject)]) MessageExpunge)
(subtree Lists MessageNew) (mailboxes misc MessageNew)
S: d OK done
C: e STATUS misc (UIDVALIDITY UIDNEXT MESSAGES)
S: * STATUS misc (UIDVALIDITY 1 UIDNEXT 999)
S: e STATUS completed
Notes:
The order of the STATUS and NOTIFY commands is changed. The original sequence is buggy, because any changes to the folder which occur between the two commands will not be noticed by the client.
Rather than just fixing it, my suggested correction also highlights the potential error -- if the authors of the RFC can do it, and especially since it's been shown as an example in the RFC until now, then it's worth making sure we highlight the problem.
4. Interaction with the IDLE Command
If IDLE [RFC2177] (as well as this extension) is supported, then
while processing any IDLE command, the server MUST send exactly the
same events as instructed by the client using the NOTIFY command.
NOTIFY makes IDLE unnecessary for some clients. If a client does not
use MSNs and '*' in commands, it can request MessageExpunge and
MessageNew for the selected mailbox by using the NOTIFY command
instead of entering the IDLE mode.
A client that uses MSNs and '*' in commands can still use the NOTIFY
command if it specifies the SELECTED-DELAYED mailbox specifier in the
NOTIFY command.
5. Event Types
Only some of the events in [RFC5423] can be expressed in IMAP, and
for some of them there are several possible ways to express the
event.
This section specifies the events of which an IMAP server can notify
an IMAP client, and how.
The server SHOULD omit notifying the client if the event is caused by
this client. For example, if the client issues CREATE and has
requested a MailboxName event that would cover the newly created
mailbox, the server SHOULD NOT notify the client of the MailboxName
change.
All event types described in this document require the 'l' and 'r'
rights (see [RFC4314]) on all observed mailboxes. Servers that don't
implement [RFC4314] should map the above rights to their access-
control model.
If the FlagChange and/or AnnotationChange events are specified,
MessageNew and MessageExpunge MUST also be specified by the client.
Otherwise, the server MUST respond with the tagged BAD response.
If one of MessageNew or MessageExpunge is specified, then both events
MUST be specified. Otherwise, the server MUST respond with the
tagged BAD response.
The client can instruct the server not to send an event by omitting
the necessary event from the list of events specified in NOTIFY SET,
by using the NONE event specifier in the NOTIFY SET, or by using
NOTIFY NONE. In particular, NOTIFY SET ... NONE can be used as a
snapshot facility by clients.
5.1. FlagChange and AnnotationChange
If the flag and/or message annotation change happens in the selected
mailbox, the server MUST notify the client by sending an unsolicited
FETCH response, which MUST include UID and FLAGS/ANNOTATION FETCH
data items. It MAY also send new FLAGS and/or OK [PERMANENTFLAGS
...] responses.
If a search context is in effect as specified in [RFC5267], an
ESEARCH ADDTO or ESEARCH REMOVEFROM will also be generated, if
appropriate. In this case, the FETCH response MUST precede the
ESEARCH response.
If the change happens in another mailbox, then the server responds
with a STATUS response. The exact content of the STATUS response
depends on various factors. If CONDSTORE [RFC4551] and/or QRESYNC
[RFC5162] are enabled by the client, then the server sends a STATUS
response that includes at least HIGHESTMODSEQ and UIDVALIDITY status
data items. If the number of messages with the \Seen flag changes,
the server MAY also include the UNSEEN data item in the STATUS
response. If CONDSTORE/QRESYNC is not enabled by the client and the
server chooses not to include the UNSEEN data item, the server does
not notify the client. When this event is requested, the server MUST
notify the client about mailbox UIDVALIDITY changes. This is done by
sending a STATUS response that includes UIDVALIDITY.
FlagChange covers the MessageRead, MessageTrash, FlagsSet, and
FlagsClear events in [RFC5423].
Example in the selected mailbox:
S: * 99 FETCH (UID 9999 FLAGS ($Junk))
And in another mailbox, with CONDSTORE in use:
S: * STATUS Lists/Lemonade (HIGHESTMODSEQ 65666665 UIDVALIDITY
101)
5.2. MessageNew
This covers both MessageNew and MessageAppend in [RFC5423].
If the new/appended message is in the selected mailbox, the server
notifies the client by sending an unsolicited EXISTS response,
followed by an unsolicited FETCH response containing the information
requested by the client. A FETCH response SHOULD NOT be generated
for a new message created by the client on this particular
connection, for instance, as the result of an APPEND or COPY command
to the selected mailbox performed by the client itself. The server
MAY also send a RECENT response, if the server marks the message as
\Recent.
Note that a single EXISTS response can be returned for multiple
MessageAppend/MessageNew events.
If a search context is in effect as specified in [RFC5267], an
ESEARCH ADDTO will also be generated, if appropriate. In this case,
the EXISTS response MUST precede the ESEARCH response. Both the
NOTIFY command and the SEARCH and SORT commands (see Section 7) can
specify attributes to be returned for new messages. These attributes
SHOULD be combined into a single FETCH response. The server SHOULD
avoid sending duplicate data. The FETCH response(s) MUST follow any
ESEARCH ADDTO responses.
If the new/appended message is in another mailbox, the server sends
an unsolicited STATUS (UIDNEXT MESSAGES) response for the relevant
mailbox. If the CONDSTORE extension [RFC4551] and/or the QRESYNC
extension [RFC5162] is enabled, the HIGHESTMODSEQ status data item
MUST be included in the STATUS response.
The client SHOULD NOT use FETCH attributes that implicitly set the
\seen flag, or that presuppose the existence of a given bodypart.
UID, MODSEQ, FLAGS, ENVELOPE, BODY.PEEK[HEADER.FIELDS... and
BODY/BODYSTRUCTURE may be the most useful attributes.
Note that if a client asks to be notified of MessageNew events with
the SELECTED mailbox specifier, the number of messages can increase
at any time, and therefore the client cannot refer to a specific
message using the MSN/UID '*'.
Example in the selected mailbox:
S: * 444 EXISTS
S: * 444 FETCH (UID 9999)
And in another mailbox, without CONDSTORE enabled:
S: * STATUS Lists/Lemonade (UIDNEXT 10002 MESSAGES 503)
5.3. MessageExpunge
If the expunged message or messages are in the selected mailbox, the
server notifies the client using EXPUNGE (or VANISHED, if [RFC5162]
is supported by the server and enabled by the client).
If a search context is in effect, as specified in [RFC5267], an
ESEARCH REMOVEFROM will also be generated, if appropriate.
If the expunged message or messages are in another mailbox, the
server sends an unsolicited STATUS (UIDNEXT MESSAGES) response for
the relevant mailbox. If the QRESYNC [RFC5162] extension is enabled,
the HIGHESTMODSEQ data item MUST be included in the STATUS response
as well.
Note that if a client requests MessageExpunge with the SELECTED
mailbox specifier, the meaning of an MSN can change at any time, so
the client cannot use MSNs in commands anymore. For example, such a
client cannot use FETCH, but has to use UID FETCH. The meaning of
'*' can also change when messages are added or expunged. A client
wishing to keep using MSNs can either use the SELECTED-DELAYED
mailbox specifier or can avoid using the MessageExpunge event
entirely.
The MessageExpunge notification covers both MessageExpunge and
MessageExpire events from [RFC5423].
Example in the selected mailbox, without QRESYNC:
S: * 444 EXPUNGE
The same example in the selected mailbox, with QRESYNC:
S: * VANISHED 5444
And in another mailbox, when QRESYNC is not enabled:
S: * STATUS misc (UIDNEXT 999 MESSAGES 554)
5.4. MailboxName
These notifications are sent if an affected mailbox name was created
(with CREATE), deleted (with DELETE), or renamed (with RENAME). For
a server that implements [RFC4314], granting or revocation of the 'l'
right to the current user on the affected mailbox MUST be considered
mailbox creation or deletion, respectively. If a mailbox is created
or deleted, the mailbox itself and its direct parent (whether it is
an existing mailbox or not) are considered to be affected.
The server notifies the client by sending an unsolicited LIST
response for each affected mailbox name. If, after the event, the
mailbox name does not refer to a mailbox accessible to the client,
the \Nonexistent flag MUST be included.
For each LISTable mailbox renamed, the server sends an extended LIST
response [RFC5258] for the new mailbox name, containing the OLDNAME
extended data item with the old mailbox name. When a mailbox is
renamed, its children are renamed too. No additional MailboxName
events are sent for children in this case. When INBOX is renamed, a
new INBOX is assumed to be created. No MailboxName event is sent for
INBOX in this case.
If the server automatically subscribes a mailbox when it is created
or renamed, then the unsolicited LIST response for each affected
subscribed mailbox name MUST include the \Subscribed attribute (see
[RFC5258]). The server SHOULD also include \HasChildren or
\HasNoChildren attributes [RFC5258] as appropriate.
Example of a newly created mailbox (or granting of the 'l' right on
the mailbox):
S: * LIST () "/" "NewMailbox"
And a deleted mailbox (or revocation of the 'l' right on the
mailbox):
S: * LIST (\NonExistent) "." "INBOX.DeletedMailbox"
Example of a renamed mailbox:
S: * LIST () "/" "NewMailbox" ("OLDNAME" ("OldMailbox"))
5.5. SubscriptionChange
The server notifies the client by sending an unsolicited LIST
response for each affected mailbox name. If and only if the mailbox
is subscribed after the event, the \Subscribed attribute (see
[RFC5258]) is included. Note that in the LIST response, all mailbox
attributes MUST be accurately computed (this differs from the
behavior of the LSUB command).
Example:
S: * LIST (\Subscribed) "/" "SubscribedMailbox"
5.6. MailboxMetadataChange
Support for this event type is OPTIONAL unless the METADATA extension
[RFC5464] is also supported by the server, in which case support for
this event type is REQUIRED.
A client willing to receive unsolicited METADATA responses as a
result of using the MailboxMetadataChange event in the NOTIFY command
doesn't have to issue ENABLE METADATA.
The server sends an unsolicited METADATA response (as per Section
4.4.2 of [RFC5464]). If possible, only the changed metadata SHOULD
be included, but if the server can't detect a change to a single
metadata item, it MAY include all metadata items set on the mailbox.
If a metadata item is deleted (set to NIL), it MUST always be
included in the METADATA response.
Example:
S: * METADATA "INBOX" /shared/comment
5.7. ServerMetadataChange
Support for this event type is OPTIONAL unless the METADATA or the
METADATA-SERVER extension [RFC5464] is also supported by the server,
in which case support for this event type is REQUIRED.
A client willing to receive unsolicited METADATA responses as a
result of using the ServerMetadataChange event in the NOTIFY command
doesn't have to issue ENABLE METADATA or ENABLE METADATA-SERVER.
The server sends an unsolicited METADATA response (as per Section
4.4.2 of [RFC5464]). Only the names of changed metadata entries
SHOULD be returned in such METADATA responses. If a metadata item is
deleted (set to NIL), it MUST always be included in the METADATA
response.
Example:
S: * METADATA "" /shared/comment
5.8. Notification Overflow
If the server is unable or unwilling to deliver as many notifications
as it is being asked to, it may disable notifications for some or all
clients. It MUST notify these clients by sending an untagged "OK
[NOTIFICATIONOVERFLOW]" response and behave as if a NOTIFY NONE
command had just been received.
Example:
S: * OK [NOTIFICATIONOVERFLOW] ...A comment can go here...
5.9. ACL (Access Control List) Changes
Even if NOTIFY succeeds, it is still possible to lose access to the
mailboxes being monitored at a later time. If this happens, the
server MUST stop monitoring these mailboxes. If access is later
granted, the server MUST restart event monitoring.
The server SHOULD return the LIST response with the \NoAccess name
attribute if and when the mailbox loses the 'l' right. Similarly,
the server SHOULD return the LIST response with no \NoAccess name
attribute if the mailbox was previously reported as having \NoAccess
and the 'l' right is later granted.
6. Mailbox Specification
Mailboxes to be monitored can be specified in several different ways.
Only 'SELECTED' and 'SELECTED-DELAYED' (Section 6.1) match the
currently selected mailbox. All other mailbox specifications affect
other (non-selected) mailboxes.
Note that multiple <event-group>s can apply to the same mailbox. The
following example demonstrates this. In this example, MessageNew and
MessageExpunge events are reported for INBOX, due to the first
<event-group>. A SubscriptionChange event will also be reported for
INBOX, due to the second <event-group>.
C: a notify set (mailboxes INBOX (Messagenew messageExpunge))
(personal (SubscriptionChange))
A typical client that supports the NOTIFY extension would ask for
events on the selected mailbox and some named mailboxes.
In the next example, the client asks for FlagChange events for all
personal mailboxes except the currently selected mailbox. This is
different from the previous example because SELECTED overrides all
other message event definitions for the currently selected mailbox
(see Section 3.1).
C: a notify set (selected (Messagenew (uid flags) messageExpunge))
(personal (MessageNew FlagChange MessageExpunge))
6.1. Mailbox Specifiers Affecting the Currently Selected Mailbox
Only one of the mailbox specifiers affecting the currently selected
mailbox can be specified in any NOTIFY command. The two such mailbox
specifiers (SELECTED and SELECTED-DELAYED) are described below.
Both refer to the mailbox that was selected using either SELECT or
EXAMINE (see [RFC3501], Sections 6.3.1 and 6.3.2). When the IMAP
connection is not in the selected state, such mailbox specifiers
don't refer to any mailbox.
The mailbox specifiers only apply to <message-event>s. It is an
error to specify other types of events with either the SELECTED or
the SELECTED-DELAYED selector.
6.1.1. Selected
The SELECTED mailbox specifier requires the server to send immediate
notifications for the currently selected mailbox about all specified
<message-event>s.
6.1.2. Selected-Delayed
The SELECTED-DELAYED mailbox specifier requires the server to delay a
MessageExpunge event until the client issues a command that allows
returning information about expunged messages (see Section 7.4.1 of
[RFC3501] for more details), for example, till a NOOP or an IDLE
command has been issued. When SELECTED-DELAYED is specified, the
server MAY also delay returning other <message-event>s until the
client issues one of the commands specified above, or it MAY return
them immediately.
6.2. Personal
Personal refers to all selectable mailboxes in the user's personal
namespace(s), as defined in [RFC2342].
6.3. Inboxes
Inboxes refers to all selectable mailboxes in the user's personal
namespace(s) to which messages may be delivered by a Message Delivery
Agent (MDA) (see [EMAIL-ARCH], particularly Section 4.3.3).
If the IMAP server cannot easily compute this set, it MUST treat
"inboxes" as equivalent to "personal".
6.4. Subscribed
Subscribed refers to all mailboxes subscribed to by the user.
If the subscription list changes, the server MUST reevaluate the
list.
6.5. Subtree
Subtree is followed by a mailbox name or list of mailbox names. A
subtree refers to all selectable mailboxes that are subordinate to
the specified mailbox plus the specified mailbox itself.
6.6. Mailboxes
Mailboxes is followed by a mailbox name or a list of mailbox names.
The server MUST NOT do a wildcard expansion. This means there is no
special treatment for the LIST wildcard characters ('*' and '%') if
they are present in mailbox names.
7. Extension to SEARCH and SORT Commands
If the server that supports the NOTIFY extension also supports
CONTEXT=SEARCH and/or CONTEXT=SORT as defined in [RFC5267], the
UPDATE return option is extended so that a client can request that
FETCH attributes be returned when a new message is added to the
context result set.
For example:
C: a00 SEARCH RETURN (COUNT UPDATE (UID BODY[HEADER.FIELDS (TO
FROM SUBJECT)])) FROM "boss"
S: * ESEARCH (TAG "a00") (COUNT 17)
S: a00 OK
[...a new message is delivered...]
S: * EXISTS 93
S: * 93 FETCH (UID 127001 BODY[HEADER.FIELDS (FROM TO SUBJECT)]
{76}
S: Subject: Re: good morning
S: From: myboss@example.org
S: To: bob@example.org
S:
S: )
S: * ESEARCH (TAG "a00") ADDTO (0 93)
Note that the EXISTS response MUST precede any FETCH responses, and
together they MUST precede the ESEARCH response.
No untagged FETCH response SHOULD be returned if a message becomes a
member of UPDATE SEARCH due to flag or annotation changes.
8. Formal Syntax
EID 1694 (Verified) is as follows:Section: 8, pg.18
Original Text:
message-event = ( "MessageNew" [SP
"(" fetch-att *(SP fetch-att) ")" ] )
[[...]]
| ;; The fett-att list may only be present for the
;; SELECTED/SELECTED-DELAYED mailbox filter
;; (<filter-mailboxes>).
Corrected Text:
message-event = ( "MessageNew" [SP
"(" fetch-att *(SP fetch-att) ")" ] )
[[...]]
| ;; The fetch-att list may only be present for the
;; SELECTED/SELECTED-DELAYED mailbox filter
;; (<filter-mailboxes>).
Notes:
Location is near bottom of page 18.
Rationale: confusing typo; s/fett/fetch/
The following syntax specification uses the Augmented Backus-Naur
Form (ABNF) notation as specified in [RFC5234]. [RFC3501] defines
the non-terminals "capability", "command-auth", "mailbox", "mailbox-
data", "resp-text-code", and "search-key". The "modifier-update"
non-terminal is defined in [RFC5267]. "mbx-list-oflag" is defined in
[RFC3501] and updated by [RFC5258].
Except as noted otherwise, all alphabetic characters are case-
insensitive. The use of upper or lower case characters to define
token strings is for editorial clarity only. Implementations MUST
accept these strings in a case-insensitive fashion. For example, the
<filter-mailboxes-selected> non-terminal value "SELECTED" must be
treated in the same way as "Selected" or "selected".
capability =/ "NOTIFY"
command-auth =/ notify
notify = "NOTIFY" SP
(notify-set / notify-none)
notify-set = "SET" [status-indicator] SP event-groups
; Replace registered notification events
; with the specified list of events
notify-none = "NONE"
; Cancel all registered notification
; events. The client is not interested
; in receiving any events.
status-indicator = SP "STATUS"
one-or-more-mailbox = mailbox / many-mailboxes
many-mailboxes = "(" mailbox *(SP mailbox) ")"
event-groups = event-group *(SP event-group)
event-group = "(" filter-mailboxes SP events ")"
;; Only <message-event>s are allowed in <events>
;; when <filter-mailboxes-selected> is used.
filter-mailboxes = filter-mailboxes-selected /
filter-mailboxes-other
filter-mailboxes-other = "inboxes" / "personal" / "subscribed" /
( "subtree" SP one-or-more-mailbox ) /
( "mailboxes" SP one-or-more-mailbox )
filter-mailboxes-selected = "selected" / "selected-delayed"
;; Apply to the currently selected mailbox only.
;; Only one of them can be specified in a NOTIFY
;; command.
events = ( "(" event *(SP event) ")" ) / "NONE"
;; As in [MSGEVENT].
;; "NONE" means that the client does not wish
;; to receive any events for the specified
;; mailboxes.
event = message-event /
mailbox-event / user-event / event-ext
message-event = ( "MessageNew" [SP
"(" fetch-att *(SP fetch-att) ")" ] )
/ "MessageExpunge"
/ "FlagChange"
/ "AnnotationChange"
;; "MessageNew" includes "MessageAppend" from
;; [MSGEVENT]. "FlagChange" is any of
;; "MessageRead", "MessageTrash", "FlagsSet",
;; "FlagsClear" [MSGEVENT]. "MessageExpunge"
;; includes "MessageExpire" [MSGEVENT].
;; MessageNew and MessageExpunge MUST always
;; be specified together. If FlagChange is
;; specified, then MessageNew and MessageExpunge
;; MUST be specified as well.
;; The fett-att list may only be present for the
;; SELECTED/SELECTED-DELAYED mailbox filter
;; (<filter-mailboxes>).
mailbox-event = "MailboxName" /
"SubscriptionChange" / "MailboxMetadataChange"
; "SubscriptionChange" includes
; MailboxSubscribe and MailboxUnSubscribe.
; "MailboxName" includes MailboxCreate,
; "MailboxDelete" and "MailboxRename".
user-event = "ServerMetadataChange"
event-ext = atom
;; For future extensions
oldname-extended-item = "OLDNAME" SP "(" mailbox ")"
;; Extended data item (mbox-list-extended-item)
;; returned in a LIST response when a mailbox is
;; renamed.
;; Note 1: the OLDNAME tag can be returned
;; with or without surrounding quotes, as per
;; mbox-list-extended-item-tag production.
resp-text-code =/ "NOTIFICATIONOVERFLOW" /
unsupported-events-code
message-event-name = "MessageNew" /
"MessageExpunge" / "FlagChange" /
"AnnotationChange"
event-name = message-event-name / mailbox-event /
user-event
unsupported-events-code = "BADEVENT"
SP "(" event-name *(SP event-name) ")"
modifier-update = "UPDATE"
[ "(" fetch-att *(SP fetch-att) ")" ]
mbx-list-oflag =/ "\NoAccess"
9. Security Considerations
It is very easy for a client to deny itself service using NOTIFY.
Asking for all events on all mailboxes may work on a small server,
but with a big server, can swamp the client's network connection or
processing capability. In the worst case, the server's processing
could also degrade the service it offers to other clients.
Server authors should be aware that if a client issues requests and
does not listen to the resulting responses, the TCP window can easily
fill up, and a careless server might block. This problem also exists
in plain IMAP; however, this extension magnifies the problem.
This extension makes it possible to retrieve messages immediately
when they are added to the mailbox. This makes it wholly impractical
to delete sensitive messages using programs like imapfilter. Using
SIEVE [RFC5228] or similar is much better.
10. IANA Considerations
The IANA has added NOTIFY to the list of IMAP extensions.
10.1. Initial LIST-EXTENDED Extended Data Item Registrations
The following entry has been added to the LIST-EXTENDED response
registry [RFC5258]:
To: iana@iana.org
Subject: Registration of OLDNAME LIST-EXTENDED extended data item
LIST-EXTENDED extended data item tag: OLDNAME
LIST-EXTENDED extended data item description: The OLDNAME extended
data item describes the old mailbox name for the mailbox
identified by the LIST response.
Which LIST-EXTENDED option(s) (and their types) causes this extended
data item to be returned (if any): none
Published specification : RFC 5465, Section 5.4.
Security considerations: none
Intended usage: COMMON
Person and email address to contact for further information: Alexey
Melnikov <Alexey.Melnikov@isode.com>
Owner/Change controller: iesg@ietf.org
11. Acknowledgments
The authors gratefully acknowledge the help of Peter Coates, Dave
Cridland, Mark Crispin, Cyrus Daboo, Abhijit Menon-Sen, Timo
Sirainen, and Eric Burger. In particular, Peter Coates contributed
lots of text and useful suggestions to this document.
Various examples are copied from other RFCs.
This document builds on one published and two unpublished drafts by
the same authors.
12. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2177] Leiba, B., "IMAP4 IDLE command", RFC 2177, June 1997.
[RFC2342] Gahrns, M. and C. Newman, "IMAP4 Namespace", RFC 2342,
May 1998.
[RFC3501] Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION
4rev1", RFC 3501, March 2003.
[RFC4314] Melnikov, A., "IMAP4 Access Control List (ACL)
Extension", RFC 4314, December 2005.
[RFC4466] Melnikov, A. and C. Daboo, "Collected Extensions to
IMAP4 ABNF", RFC 4466, April 2006.
[RFC4551] Melnikov, A. and S. Hole, "IMAP Extension for
Conditional STORE Operation or Quick Flag Changes
Resynchronization", RFC 4551, June 2006.
[RFC5162] Melnikov, A., Cridland, D., and C. Wilson, "IMAP4
Extensions for Quick Mailbox Resynchronization", RFC
5162, March 2008.
[RFC5234] Crocker, D., Ed., and P. Overell, "Augmented BNF for
Syntax Specifications: ABNF", STD 68, RFC 5234, January
2008.
[RFC5258] Leiba, B. and A. Melnikov, "Internet Message Access
Protocol version 4 - LIST Command Extensions", RFC 5258,
June 2008.
[RFC5267] Cridland, D. and C. King, "Contexts for IMAP4", RFC
5267, July 2008.
[RFC5423] Newman, C. and R. Gellens, "Internet Message Store
Events", RFC 5423, Month 2009.
[RFC5464] Daboo, C., "The IMAP METADATA Extension", RFC 5464,
February 2009.
13. Informative References
[RFC5228] Guenther, P., Ed., and T. Showalter, Ed., "Sieve: An
Email Filtering Language", RFC 5228, January 2008.
[EMAIL-ARCH] Crocker, D., "Internet Mail Architecture", Work in
Progress, October 2008.
Authors' Addresses
Arnt Gulbrandsen
Oryx Mail Systems GmbH
Schweppermannstr. 8
D-81671 Muenchen
Germany
EMail: arnt@oryx.com
Curtis King
Isode Ltd
5 Castle Business Village
36 Station Road
Hampton, Middlesex TW12 2BX
UK
EMail: Curtis.King@isode.com
Alexey Melnikov
Isode Ltd
5 Castle Business Village
36 Station Road
Hampton, Middlesex TW12 2BX
UK
EMail: Alexey.Melnikov@isode.com