WDIFF

draft-ietf-imapext-condstore-09.txt --> rfc4551.txt

Network Working Group A. Melnikov
Document: draft-ietf-imapext-condstore-09.txt
Request for Comments: 4551 Isode Ltd.
Expires: August 2006
Updates: 3501 S. Hole
Category: Standards Track ACI WorldWide/MessagingDirect
February
June 2006

IMAP Extension for Conditional STORE operation Operation
or quick flag changes resynchronization Quick Flag Changes Resynchronization

Status of this This Memo

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Abstract

Often, multiple IMAP (RFC 3501) clients need to coordinate changes to
a common IMAP mailbox. Examples include different clients working on
behalf of the same user, and multiple users accessing shared
mailboxes. These clients need a mechanism to synchronize state
changes for messages within the mailbox. They must be able to
guarantee that only one client can change message state (e.g.,
message flags) at any time. An example of such an application is use
of an IMAP mailbox as a message queue with multiple dequeueing
clients.

The Conditional Store facility provides a protected update mechanism
for message state information that can detect and resolve conflicts
between multiple writing mail clients.

The Conditional Store facility also allows a client to quickly
resynchronize mailbox flag changes.

This document defines an extension to IMAP (RFC 3501).

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Table of Contents

1. Introduction and Overview ................................. 3
2. Conventions Used in This Document ......................... X
2 Introduction and Overview ................................. X
3 5
3. IMAP Protocol Changes ..................................... X
3.1 6
3.1. New OK untagged responses for SELECT and EXAMINE ......... X
3.1.1 6
3.1.1. HIGHESTMODSEQ response code ............................ X
3.1.2 6
3.1.2. NOMODSEQ response code ................................. X
3.2 7
3.2. STORE and UID STORE Commands ............................. X 7
3.3 FETCH and UID FETCH Commands ............................. X
3.3.1 ..............................13
3.3.1. CHANGEDSINCE FETCH modifier ............................ X
3.3.2 ............................13
3.3.2. MODSEQ message data item in FETCH Command .............. X
3.4 ..............14
3.4. MODSEQ search criterion in SEARCH ........................ X
3.5 ........................16
3.5. Modified SEARCH untagged response ........................ X
3.6 ........................17
3.6. HIGHESTMODSEQ status data items .......................... X
3.7 ..........................17
3.7. CONDSTORE parameter to SELECT and EXAMINE ................ X
3.8 ................18
3.8. Additional quality of implementation issues .............. X
4 ..............18
4. Formal Syntax ............................................. X
5 .............................................19
5. Server implementation considerations ...................... X
6 ......................21
6. Security Considerations ................................... X
7 ...................................22
7. IANA Considerations .......................................22
8. References ................................................ X
7.1 ................................................23
8.1. Normative References ..................................... X
7.2 .....................................23
8.2. Informative References ................................... X
8 IANA Considerations ....................................... X
9 Acknowledgments ........................................... X
10 Author's Addresses ........................................ X
11 Intellectual Property Rights .............................. X
12 Full Copyright Statement .................................. X ...................................23
9. Acknowledgements ..........................................23

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1. Conventions Used in This Document

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", Introduction and "OPTIONAL" Overview

The Conditional STORE extension is present in this
document are to be interpreted any IMAP4
implementation that returns "CONDSTORE" as described in RFC 2119 [KEYWORDS].

In examples, lines beginning with "S:" are sent by the IMAP server, and
lines beginning with "C:" are sent by the client. Line breaks may appear
in example commands solely for editorial clarity; when present in
the actual message they are represented by "CRLF".

Formal syntax is defined using ABNF [ABNF].

The term "metadata" or "metadata item" is used throughout this document.
It refers to any system or user defined keyword. Future documents
may extend "metadata" to include other dynamic message data.

Some IMAP mailboxes are private, accessible only to the owning user.
Other mailboxes are not, either because the owner has set an ACL
[ACL] which permits access by other users, or because it is a
shared mailbox. Let's call a metadata item "shared" for the mailbox
if any changes to the metadata items are persistent and visible to all
other users accessing the mailbox. Otherwise the metadata item is called
"private". Note, that private metadata items are still visible to all
sessions accessing the mailbox as the same user. Also note, that different
mailboxes may have different metadata items as shared.

See the next section for the definition of a "CONDSTORE-aware client"
and a "CONDSTORE enabling command".

2. Introduction and Overview

The Conditional STORE extension is present in any IMAP4 implementation
which returns "CONDSTORE" as one of the supported capabilities one of the supported
capabilities in the CAPABILITY command response.

An IMAP server that supports this extension MUST associate a positive
unsigned 64-bit value called a modification sequence (mod-sequence)
with every IMAP message. This is an opaque value updated by the
server whenever a metadata item is modified. The server MUST
guarantee that each STORE command performed on the same mailbox, including mailbox
(including simultaneous stores to different metadata items from
different connections, connections) will get a different mod-sequence value.
Also, for any two successful STORE operations performed in the same
session on the same mailbox, the mod-sequence of the second completed
operation MUST be greater than the mod-sequence of the first
completed. Note that the latter rule disallows the use of the system
clock as a mod-sequence, because if system time changes (e.g., a an NTP
[NTP] client adjusting the time), the next generated value might be
less than the previous one.

Mod-sequences allow a client that supports the CONDSTORE extension to
determine if a message metadata has changed since some known moment.
Whenever the state of a flag changes (i.e., the flag is added where
previously it wasn't set, or the flag is removed and before it was
set) the value of the modification sequence for the message MUST be
updated. Adding the flag when it is already present or removing when
it is not present SHOULD NOT change the mod-sequence.

When a message is appended to a mailbox (via the IMAP APPEND command,
COPY to the mailbox mailbox, or using an external mechanism) the server
generates a new modification sequence that is higher than the highest
modification sequence of all messages in the mailbox and assigns it
to the appended message.

The server MAY store separate (per message) (per-message) modification sequence
values for different metadata items. If the server does so, per per-
message mod-sequence is the highest mod-sequence of all metadata
items for the specified message.

The server that supports this extension is not required to be able to
store mod-sequences for every available mailbox. Section 3.1.2
describes how the server may act if a particular mailbox doesn't
support the persistent storage of mod-sequences.

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This extension makes the following changes to the IMAP4 protocol:

a) adds UNCHANGEDSINCE STORE modifier modifier.

b) adds the MODIFIED response code which should be used with an OK
response to the STORE command. (It can also be used in a NO
response.)

c) adds a new MODSEQ message data item for use with the FETCH command
command.

d) adds CHANGEDSINCE FETCH modifier modifier.

e) adds a new MODSEQ search criterion criterion.

f) extends the syntax of untagged SEARCH responses to include mod-sequence
mod-sequence.

g) adds new OK untagged responses for the SELECT and EXAMINE commands
commands.

h) defines an additional parameter to SELECT/EXAMINE commands commands.

i) adds the HIGHESTMODSEQ status data item to the STATUS command command.

A client supporting CONDSTORE extension indicates its willingness to
receive mod-sequence updates in all untagged FETCH responses by issuing
issuing:

- a SELECT or EXAMINE command with the CONDSTORE parameter, or
- a STATUS (HIGHESTMODSEQ) command,
or
- a FETCH, FETCH or SEARCH command that includes the MODSEQ message data
item,
- a FETCH command with the CHANGEDSINCE modifier, or
- a STORE command with the UNCHANGEDSINCE modifier.

The server MUST include mod-sequence data in all subsequent untagged
FETCH
responses, responses (until the connection is closed), whether they were
caused by a regular STORE, a STORE with UNCHANGEDSINCE modifier, or
an external agent, until the connection is closed. agent.

This document uses the term "CONSTORE-aware "CONDSTORE-aware client" to refer to a
client that announces its willingness to receive mod-sequence updates
as described above. The term "CONDSTORE enabling command" will refer
any of the commands listed above. A future extension to this
document may extend the list of CONDSTORE enabling commands. A first
CONDSTORE enabling command executed in the session MUST cause the

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server to return HIGHESTMODSEQ (section (Section 3.1.1) unless the server has
sent NOMODSEQ (section (Section 3.1.2) response code when the currently
selected mailbox was selected.

The rest of this document describes the protocol changes more
rigorously.

3. IMAP Protocol Changes

3.1. New OK untagged responses for SELECT and EXAMINE

2. Conventions Used in This document adds two new response codes HIGHESTMODSEQ Document

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and NOMODSEQ.
One of those response codes MUST "OPTIONAL" in this
document are to be returned interpreted as described in RFC 2119 [KEYWORDS].

In examples, lines beginning with "S:" are sent by the OK untagged
response IMAP server,
and lines beginning with "C:" are sent by the client. Line breaks
may appear in example commands solely for a successful SELECT/EXAMINE command.

When opening a mailbox editorial clarity; when
present in the server must check if actual message, they are represented by "CRLF".

Formal syntax is defined using ABNF [ABNF].

The term "metadata" or "metadata item" is used throughout this
document. It refers to any system or user-defined keyword. Future
documents may extend "metadata" to include other dynamic message
data.

Some IMAP mailboxes are private, accessible only to the mailbox supports owning user.
Other mailboxes are not, either because the persistent storage of mod-sequences. If owner has set an Access
Control List [ACL] that permits access by other users, or because it
is a shared mailbox. Let's call a metadata item "shared" for the
mailbox supports if any changes to the metadata items are persistent storage of mod-sequences and mailbox open operation succeeds,
visible to all other users accessing the server MUST send mailbox. Otherwise, the OK untagged response
metadata item is called "private". Note that private metadata items
are still visible to all sessions accessing the mailbox as the same
user. Also note that different mailboxes may have different metadata
items as shared.

See Section 1 for the definition of a "CONDSTORE-aware client" and a
"CONDSTORE enabling command".

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3. IMAP Protocol Changes

3.1. New OK Untagged Responses for SELECT and EXAMINE

This document adds two new response codes, HIGHESTMODSEQ and
NOMODSEQ. One of those response codes MUST be returned in the OK
untagged response for a successful SELECT/EXAMINE command.

When opening a mailbox, the server must check if the mailbox supports
the persistent storage of mod-sequences. If the mailbox supports the
persistent storage of mod-sequences and the mailbox open operation
succeeds, the server MUST send the OK untagged response including
HIGHESTMODSEQ response code. If the persistent storage for the
mailbox is not supported, the server MUST send the OK untagged
response including NOMODSEQ response code instead.

3.1.1. HIGHESTMODSEQ response code Response Code

This document adds a new response code that is returned in the OK
untagged response for the SELECT and EXAMINE commands. A server
supporting the persistent storage of mod-sequences for the mailbox
MUST send the OK untagged response including HIGHESTMODSEQ response
code with every successful SELECT or EXAMINE command:

OK [HIGHESTMODSEQ <mod-sequence-value>]

Where

where <mod-sequence-value> is the highest mod-sequence value of
all messages in the mailbox. When the server changes UIDVALIDITY
for a mailbox, it doesn't have to keep the same HIGHESTMODSEQ for
the mailbox.

A disconnected client can use the value of HIGHESTMODSEQ to check if
it has to refetch metadata from the server. If the UIDVALIDITY value
has changed for the selected mailbox, the client MUST delete the
cached value of HIGHESTMODSEQ. If UIDVALIDITY for the mailbox is the same
same, and if the HIGHESTMODSEQ value stored in the client's cache is
less than the value returned by the server, then some metadata items
on the server have changed since the last synchronization, and the
client needs to update its cache. The client MAY use SEARCH MODSEQ as described in section 3.4
(Section 3.4) to find out exactly which metadata items have changed. Alternatively
Alternatively, the client MAY issue FETCH with the CHANGEDSINCE
modifier (section (Section 3.3.1) in order to fetch data for all messages that
have metadata items changed since some known modification sequence.

Example:

Example 1:

C: A142 SELECT INBOX
S: * 172 EXISTS

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S: * 1 RECENT
S: * OK [UNSEEN 12] Message 12 is first unseen
S: * OK [UIDVALIDITY 3857529045] UIDs valid
S: * OK [UIDNEXT 4392] Predicted next UID
S: * FLAGS (\Answered \Flagged \Deleted \Seen \Draft)
S: * OK [PERMANENTFLAGS (\Deleted \Seen \*)] Limited
S: * OK [HIGHESTMODSEQ 715194045007]
S: A142 OK [READ-WRITE] SELECT completed

3.1.2. NOMODSEQ response code Response Code

A server that doesn't support the persistent storage of mod-sequences
for the mailbox MUST send the OK untagged response including NOMODSEQ
response code with every successful SELECT or EXAMINE command.

Example: A
server that returned NOMODSEQ response code for a mailbox, which
subsequently receives one of the following commands while the mailbox
is selected:

- a FETCH command with the CHANGEDSINCE modifier,
- a FETCH or SEARCH command that includes the MODSEQ message data
item, or
- a STORE command with the UNCHANGEDSINCE modifier

MUST reject any such command with the tagged BAD response.

Example 2:

C: A142 SELECT INBOX
S: * 172 EXISTS
S: * 1 RECENT
S: * OK [UNSEEN 12] Message 12 is first unseen
S: * OK [UIDVALIDITY 3857529045] UIDs valid
S: * OK [UIDNEXT 4392] Predicted next UID
S: * FLAGS (\Answered \Flagged \Deleted \Seen \Draft)
S: * OK [PERMANENTFLAGS (\Deleted \Seen \*)] Limited
S: * OK [NOMODSEQ] Sorry, this mailbox format doesn't support
modsequences
S: A142 OK [READ-WRITE] SELECT completed

3.2. STORE and UID STORE Commands

This document defines the following STORE modifier (see section Section 2.5
of [IMAPABNF]):

UNCHANGEDSINCE <mod-sequence>

For each message specified in the message set set, the server performs
the following. If the mod-sequence of any metadata item of the

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message is equal or less than the specified UNCHANGEDSINCE value,
then the requested operation (as described by the message data
item) is performed. If the operation is successful successful, the server
MUST update the mod-sequence attribute of the message. An
untagged FETCH response MUST be sent, even if the .SILENT suffix
is specified specified, and the response MUST include the MODSEQ message
data item. This is required to update the client's cache with the
correct mod-sequence values. See section Section 3.3.2 for more details.

However, if the mod-sequence of any metadata item of the message
is greater than the specified UNCHANGEDSINCE value, than then the
requested operation MUST NOT be performed. In this case, the
mod-sequence attribute of the message is not updated, and the
message number (or unique identifier in the case of the UID STORE
command) is added to the list of messages that failed the
UNCHANGESINCE test.

When the server finished performing the operation on all the
messages in the message set, it checks for a non-empty list of
messages that failed the UNCHANGESINCE test. If this list is
non-empty, the server MUST return in the tagged response a
MODIFIED response code. The MODIFIED response code includes the
message set (for STORE) or set of UIDs (for UID STORE) of all
messages that failed the UNCHANGESINCE test.

Example : 3:

All messages pass the UNCHANGESINCE test.

C: a103 UID STORE 6,4,8 (UNCHANGEDSINCE 12121230045)
+FLAGS.SILENT (\Deleted)
S: * 1 FETCH (UID 4 MODSEQ (12121231000))
S: * 2 FETCH (UID 6 MODSEQ (12121230852))
S: * 4 FETCH (UID 8 MODSEQ (12121130956))
S: a103 OK Conditional Store completed

Example:

Example 4:

C: a104 STORE * (UNCHANGEDSINCE 12121230045) +FLAGS.SILENT
(\Deleted $Processed)
S: * 50 FETCH (MODSEQ (12111230047))
S: a104 OK Store (conditional) completed

Example:

Example 5:

C: c101 STORE 1 (UNCHANGEDSINCE 12121230045) -FLAGS.SILENT
(\Deleted)
S: * OK [HIGHESTMODSEQ 12111230047]

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S: * 50 FETCH (MODSEQ (12111230048))
S: c101 OK Store (conditional) completed

HIGHESTMODSEQ response code was sent by the server presumably
because this was the first CONDSTORE enabling command.

Example:

Example 6:

In spite of the failure of the conditional STORE operation for
message 7, the server continues to process the conditional STORE
in order to find all messages which that fail the test.

C: d105 STORE 7,5,9 (UNCHANGEDSINCE 320162338)
+FLAGS.SILENT (\Deleted)
S: * 5 FETCH (MODSEQ (320162350))
S: d105 OK [MODIFIED 7,9] Conditional STORE failed

Example:

Example 7:

Same as above, but the server follows the SHOULD recommendation in section
Section 6.4.6 of [IMAP4].

C: d105 STORE 7,5,9 (UNCHANGEDSINCE 320162338)
+FLAGS.SILENT (\Deleted)
S: * 7 FETCH (MODSEQ (320162342) FLAGS (\Seen \Deleted))
S: * 5 FETCH (MODSEQ (320162350))
S: * 9 FETCH (MODSEQ (320162349) FLAGS (\Answered))
S: d105 OK [MODIFIED 7,9] Conditional STORE failed

Use of UNCHANGEDSINCE with a modification sequence of 0 always
fails if the metadata item exists. A system flag MUST always be
considered existent, whether it was set or not.

Example:

Example 8:

C: a102 STORE 12 (UNCHANGEDSINCE 0)
+FLAGS.SILENT ($MDNSent)
S: a102 OK [MODIFIED 12] Conditional STORE failed

The client has tested the presence of the $MDNSent user defined user-defined
keyword.

Note: A client trying to make an atomic change to the state of a
particular metadata item (or a set of metadata items) should be
prepared to deal with the case when the server returns the MODIFIED
response code if the state of the metadata item being watched hasn't
changed (but the state of some other metadata item has). This is
necessary, because some servers don't store separate mod-sequences

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RFC 4551 IMAP Extension for Conditional STORE June 2006

for different metadata items. However, a server implementation
SHOULD avoid generating spurious MODIFIED responses for +FLAGS/-FLAGS
STORE operations, even when the server stores a single mod-sequence
per message. Section 5 describes how this can be achieved.

Unless the server has included an unsolicited FETCH to update
client's knowledge about message(s) messages that has have failed the UNCHANGEDSINCE
test, upon the receipt of the MODIFIED response code code, the client SHOULD
try to figure out if the required metadata items have indeed changed
by issuing FETCH or NOOP command. It is RECOMMENDED that the server
avoids the need for the client to do that by sending an unsolicited
FETCH response
(see two following examples). (Examples 9 and 10).

If the required metadata items haven't changed changed, the client SHOULD
retry the command with the new modsequence. mod-sequence. The client SHOULD allow
for a configurable but reasonable number of retries (at least 2).

Example:

Example 9:

In the example below below, the server returns the MODIFIED response
code without sending information describing why the STORE
UNCHANGEDSINCE operation has failed.

C: a106 STORE 100:150 (UNCHANGEDSINCE 212030000000)
+FLAGS.SILENT ($Processed)
S: * 100 FETCH (MODSEQ (303181230852))
S: * 102 FETCH (MODSEQ (303181230852))
...
S: * 150 FETCH (MODSEQ (303181230852))
S: a106 OK [MODIFIED 101] Conditional STORE failed

the

The flag $Processed was set on the message 101 ... 101...

C: a107 NOOP
S: * 101 FETCH (MODSEQ (303011130956) FLAGS ($Processed))
S: a107 OK

Or the flag hasn't changed, but another has (note, (note that this server
behaviour is discouraged. Server implementors implementers should also see
section 5) ...
Section 5)...

C: b107 NOOP
S: * 101 FETCH (MODSEQ (303011130956) FLAGS (\Deleted \Answered))
S: b107 OK

... and

...and the client retries the operation for the message 101 with
the updated UNCHANGEDSINCE value

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C: b108 STORE 101 (UNCHANGEDSINCE 303011130956)
+FLAGS.SILENT ($Processed)
S: * 101 FETCH (MODSEQ (303181230852))
S: b108 OK Conditional Store completed

Example:

Example 10:

Same as above, but the server avoids the need for the client to
poll for changes.

the

The flag $Processed was set on the message 101 by another client ...
client...

C: a106 STORE 100:150 (UNCHANGEDSINCE 212030000000)
+FLAGS.SILENT ($Processed)
S: * 100 FETCH (MODSEQ (303181230852))
S: * 101 FETCH (MODSEQ (303011130956) FLAGS ($Processed))
S: * 102 FETCH (MODSEQ (303181230852))
...
S: * 150 FETCH (MODSEQ (303181230852))
S: a106 OK [MODIFIED 101] Conditional STORE failed

Or the flag hasn't changed, but another has (note, (note that this server
behaviour is discouraged. Server implementors implementers should also see
section 5) ...
Section 5)...

C: a106 STORE 100:150 (UNCHANGEDSINCE 212030000000)
+FLAGS.SILENT ($Processed)
S: * 100 FETCH (MODSEQ (303181230852))
S: * 101 FETCH (MODSEQ (303011130956) FLAGS (\Deleted \Answered))
S: * 102 FETCH (MODSEQ (303181230852))
...
S: * 150 FETCH (MODSEQ (303181230852))
S: a106 OK [MODIFIED 101] Conditional STORE failed

... and

...and the client retries the operation for the message 101 with
the updated UNCHANGEDSINCE value

C: b108 STORE 101 (UNCHANGEDSINCE 303011130956)
+FLAGS.SILENT ($Processed)
S: * 101 FETCH (MODSEQ (303181230852))
S: b108 OK Conditional Store completed

Or the flag hasn't changed, but another has (nice server
behaviour. Server implementors implementers should also see section 5) ... Section 5)...

C: a106 STORE 100:150 (UNCHANGEDSINCE 212030000000)
+FLAGS.SILENT ($Processed)

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S: * 100 FETCH (MODSEQ (303181230852))
S: * 101 FETCH (MODSEQ (303011130956) FLAGS ($Processed \Deleted
\Answered))
S: * 102 FETCH (MODSEQ (303181230852))
...
S: * 150 FETCH (MODSEQ (303181230852))
S: a106 OK Conditional STORE completed

Example:

Example 11:

The following example is based on the example from the section Section
4.2.3 of [RFC-2180] and demonstrates that the MODIFIED response
code may be also returned in the tagged NO response.

Client tries to conditionally STORE flags on a mixture of expunged
and non-expunged messages, messages; one message fails the UNCHANGEDSINCE
test.

C: B001 STORE 1:7 (UNCHANGEDSINCE 320172338) +FLAGS (\SEEN)
S: * 1 FETCH (MODSEQ (320172342) FLAGS (\SEEN))
S: * 3 FETCH (MODSEQ (320172342) FLAGS (\SEEN))
S: B001 NO [MODIFIED 2] Some of the messages no longer exist.

C: B002 NOOP
S: * 4 EXPUNGE
S: * 4 EXPUNGE
S: * 4 EXPUNGE
S: * 4 EXPUNGE
S: * 2 FETCH (MODSEQ (320172340) FLAGS (\Deleted \Answered))
S: B002 OK NOOP Completed.

By receiving FETCH responses for messages 1 and 3, and EXPUNGE
responses that indicate that messages 4:7 4 through 7 have been
expunged, the client retries the operation only for the message 2.
The updated UNCHANGEDSINCE value is used.

C: b003 STORE 2 (UNCHANGEDSINCE 320172340) +FLAGS (\Seen)
S: * 2 FETCH (MODSEQ (320180050))
S: b003 OK Conditional Store completed

Note: If a message is specified multiple times in the message set,
and the server doesn't internally eliminate duplicates from the
message set, it MUST NOT fail the conditional STORE operation for the
second (or subsequent) occurrence of the message if the operation
completed successfully for the first occurrence. For example, if the
client specifies:

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e105 STORE 7,3:9 (UNCHANGEDSINCE 12121230045)
+FLAGS.SILENT (\Deleted)

the server must not fail the operation for message 7 as part of
processing "3:9" if it succeeded when message 7 was processed the
first time.

Once the client specified the UNCHANGEDSINCE modifier in a STORE
command, the server MUST include the MODSEQ fetch response data items
in all subsequent unsolicited FETCH responses.

This document also changes the behaviour of the server when it has
performed a STORE or UID STORE command and the UNCHANGEDSINCE
modifier is not specified. If the operation is successful for a
message, the server MUST update the mod-sequence attribute of the
message. The server is REQUIRED to include the mod-sequence value
whenever it decides to send the unsolicited FETCH response to all
CONDSTORE-aware clients that have opened the mailbox containing the
message.

Server implementors implementers should also see section Section 3.8 for additional
quality of implementation issues related to the STORE command.

3.3. FETCH and UID FETCH Commands

3.3.1. CHANGEDSINCE FETCH modifier Modifier

This document defines the following FETCH modifier (see section Section 2.4
of [IMAPABNF]):

CHANGEDSINCE <mod-sequence>

CHANGEDSINCE FETCH modifier allows to create a further subset of
the list of messages described by sequence set. The information
described by message data items is only returned for messages that
have mod-sequence bigger than <mod-sequence>.

When CHANGEDSINCE FETCH modifier is specified, it implicitly adds
MODSEQ FETCH message data item (section (Section 3.3.2).

Example:

Example 12:

C: s100 UID FETCH 1:* (FLAGS) (CHANGEDSINCE 12345)
S: * 1 FETCH (UID 4 MODSEQ (65402) FLAGS (\Seen))
S: * 2 FETCH (UID 6 MODSEQ (75403) FLAGS (\Deleted))
S: * 4 FETCH (UID 8 MODSEQ (29738) FLAGS ($NoJunk $AutoJunk
$MDNSent))
S: s100 OK FETCH completed

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3.3.2. MODSEQ message data item Message Data Item in FETCH Command

This extension adds a MODSEQ message data item to the FETCH command.
The MODSEQ message data item allows clients to retrieve mod-sequence
values for a range of messages in the currently selected mailbox.

Once the client specified the MODSEQ message data item in a FETCH
request, the server MUST include the MODSEQ fetch response data items
in all subsequent unsolicited FETCH responses.

Syntax: MODSEQ

The MODSEQ message data item causes the server to return MODSEQ
fetch response data items.

Syntax: MODSEQ ( <permsg-modsequence> )

MODSEQ response data items contain per-message mod-sequences.

The MODSEQ response data item is returned if the client issued
FETCH with MODSEQ message data item. It also allows the server to
notify the client about mod-sequence changes caused by conditional
STOREs (section (Section 3.2) and/or changes caused by external sources.

Example:

Example 13:

C: a FETCH 1:3 (MODSEQ)
S: * 1 FETCH (MODSEQ (624140003))
S: * 2 FETCH (MODSEQ (624140007))
S: * 3 FETCH (MODSEQ (624140005))
S: a OK Fetch complete

In this example example, the client requests per message per-message mod-sequences for
a set of messages.

When a flag for a message is modified in a different session, the
server sends an unsolicited FETCH response containing the mod-sequence mod-
sequence for the message.

Example:

Example 14:

(Session 1, authenticated as a user "alex"). The user adds a
shared flag \Deleted:

C: A142 SELECT INBOX
...
S: * FLAGS (\Answered \Flagged \Deleted \Seen \Draft)
S: * OK [PERMANENTFLAGS (\Answered \Deleted \Seen \*)] Limited

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...

C: A160 STORE 7 +FLAGS.SILENT (\Deleted)
S: * 7 FETCH (MODSEQ (2121231000))
S: A160 OK Store completed

(Session 2, also authenticated as the user "alex"). Any changes
to flags are always reported to all sessions authenticated as the
same user as in the session 1.

C: C180 NOOP
S: * 7 FETCH (FLAGS (\Deleted \Answered) MODSEQ (12121231000))
S: C180 OK Noop completed

(Session 3, authenticated as a user "andrew"). As \Deleted is a
shared flag, changes in the session 1 are also reported in the session 3:

C: D210 NOOP
S: * 7 FETCH (FLAGS (\Deleted \Answered) MODSEQ (12121231000))
S: D210 OK Noop completed

The user modifies a private flag \Seen in the session 1 ... 1...

C: A240 STORE 7 +FLAGS.SILENT (\Seen)
S: * 7 FETCH (MODSEQ (12121231777))
S: A240 OK Store completed

... which

...which is only reported in the session 2 ... 2...

C: C270 NOOP
S: * 7 FETCH (FLAGS (\Deleted \Answered \Seen) MODSEQ
(12121231777))
S: C270 OK Noop completed

... but

...but not in the session 3.

C: D300 NOOP
S: D300 OK Noop completed

And finally finally, the user removes flags \Answered (shared) and \Seen
(private) in the session 1.

C: A330 STORE 7 -FLAGS.SILENT (\Answered \Seen)
S: * 7 FETCH (MODSEQ (12121245160))
S: A330 OK Store completed

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Both changes are reported in the session 2 ... 2...

C: C360 NOOP
S: * 7 FETCH (FLAGS (\Deleted) MODSEQ (12121245160))
S: C360 OK Noop completed

... and

...and only changes to shared flags are reported in session 3.

C: D390 NOOP
S: * 7 FETCH (FLAGS (\Deleted) MODSEQ (12121245160))
S: D390 OK Noop completed

Server implementors implementers should also see section Section 3.8 for additional
quality of implementation issues related to the FETCH command.

3.4. MODSEQ search criterion Search Criterion in SEARCH

The MODSEQ criterion for the SEARCH command allows a client to search
for the metadata items that were modified since a specified moment.

Syntax: MODSEQ [<entry-name> <entry-type-req>] <mod-sequence-valzer>

Messages that have modification values which that are equal to or
greater than <mod-sequence-valzer>. This allows a client, for
example, to find out which messages contain metadata items that
have changed since the last time it updated its disconnected
cache. The client may also specify <entry-name> (name of metadata
item) and <entry-type-req> (type of metadata item) before
<mod-sequence-valzer>. <entry-type-req> can be one of "shared",
"priv" (private) (private), or "all". The latter means that the server
should use the biggest value among "priv" and "shared" mod-sequences mod-
sequences for the metadata item. If the server doesn't store
internally separate mod-sequences for different metadata items, it
MUST ignore <entry-name> and <entry-type-req>. Otherwise Otherwise, the
server should use them to narrow down the search.

For a flag <flagname> <flagname>, the corresponding <entry-name> has a form
"/flags/<flagname>" as defined in [IMAPABNF]. Note, Note that the
leading "\" character that denotes a system flag has to be escaped
as per Section 4.3 of [IMAP4], as the <entry-name> uses syntax for
quoted strings.

If client specifies a MODSEQ criterion in a SEARCH command and the
server returns a non-empty SEARCH result, the server MUST also append
(to the end of the untagged SEARCH response) the highest mod-sequence
for all messages being returned. See also section Section 3.5.

Example:

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RFC 4551 IMAP Extension for Conditional STORE June 2006

Example 15:

C: a SEARCH MODSEQ "/flags/\\draft" all 620162338
S: * SEARCH 2 5 6 7 11 12 18 19 20 23 (MODSEQ 917162500)
S: a OK Search complete

In the above example, the message numbers of any messages
containing the string "IMAP4" in the "value" attribute of the
"/comment" entry and having a mod-sequence equal to or greater
than 620162338 for the "\Draft" flag are returned in the search
results.

Example:

Example 16:

C: t SEARCH OR NOT MODSEQ 720162338 LARGER 50000
S: * SEARCH
S: t OK Search complete, nothing found

3.5. Modified SEARCH untagged response Untagged Response

Data: zero or more numbers
mod-sequence value (omitted if no match)

This document extends syntax of the untagged SEARCH response to
include the highest mod-sequence for all messages being returned.

If a client specifies a MODSEQ criterion in a SEARCH (or UID SEARCH)
command and the server returns a non-empty SEARCH result, the server
MUST also append (to the end of the untagged SEARCH response) the
highest mod-sequence for all messages being returned. See section Section
3.4 for examples.

3.6. HIGHESTMODSEQ status data items Status Data Items

This document defines a new status data item:

HIGHESTMODSEQ

The highest mod-sequence value of all messages in the mailbox.
This is the same value that is returned by the server in the
HIGHESTMODSEQ response code in an OK untagged response (see section
Section 3.1.1).

Example: If the server doesn't support the persistent
storage of mod-sequences for the mailbox (see Section 3.1.2), the
server MUST return 0 as the value of HIGHESTMODSEQ status data
item.

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Example 17:

C: A042 STATUS blurdybloop (UIDNEXT MESSAGES HIGHESTMODSEQ)
S: * STATUS blurdybloop (MESSAGES 231 UIDNEXT 44292
HIGHESTMODSEQ 7011231777)
S: A042 OK STATUS completed

3.7. CONDSTORE parameter Parameter to SELECT and EXAMINE

The CONDSTORE extension defines a single optional select parameter parameter,
"CONDSTORE", which tells the server that it MUST include the MODSEQ
fetch response data items in all subsequent unsolicited FETCH
responses.

The CONDSTORE parameter to SELECT/EXAMINE helps to avoid a race
condition that might arise when a one or more metadata item(s) is(are) items are
modified in another session after the server has sent the
HIGHESTMODSEQ response code and before the client was able to issue a
CONDSTORE enabling command.

Example:

Example 18:

C: A142 SELECT INBOX (CONDSTORE)
S: * 172 EXISTS
S: * 1 RECENT
S: * OK [UNSEEN 12] Message 12 is first unseen
S: * OK [UIDVALIDITY 3857529045] UIDs valid
S: * OK [UIDNEXT 4392] Predicted next UID
S: * FLAGS (\Answered \Flagged \Deleted \Seen \Draft)
S: * OK [PERMANENTFLAGS (\Deleted \Seen \*)] Limited
S: * OK [HIGHESTMODSEQ 715194045007]
S: A142 OK [READ-WRITE] SELECT completed, CONDSTORE is now enabled

3.8. Additional quality of implementation issues. Quality-of-Implementation Issues

Server implementations should follow the following rule, which
applies to any successfully completed STORE/UID STORE (with and
without UNCHANGEDSINCE modifier), as well as to a FETCH command which that
implicitly sets \Seen flag:

Adding the flag when it is already present or removing when it is
not present SHOULD NOT change the mod-sequence.

This will prevent spurious client synchronization requests.

However note that client implementors MUST NOT rely

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RFC 4551 IMAP Extension for Conditional STORE June 2006

However, note that client implementers MUST NOT rely on this server behaviour.
Client
behavior. A client can't distinguish between the case when a server
has violated the SHOULD mentioned above, or and that when one or more client(s) setting
clients set and unsetting unset (or unsetting unset and
setting) set) the flag in another session(s). session.

4. Formal Syntax

The following syntax specification uses the Augmented Backus-Naur
Form (ABNF) [ABNF] notation. Elements not defined here can be found
in the formal syntax of the ABNF [ABNF], IMAP [IMAP4], and IMAP ABNF
extensions [IMAPABNF] specifications.

Except as noted otherwise, all alphabetic characters are case-
insensitive. The use of upper upper- or lower case lowercase characters to define
token strings is for editorial clarity only. Implementations MUST
accept these strings in a case-insensitive fashion.

capability =/ "CONDSTORE"

status-att =/ "HIGHESTMODSEQ"
;; extends non-terminal defined in RFC 3501.

status-att-val =/ "HIGHESTMODSEQ" SP mod-sequence-value mod-sequence-valzer
;; extends non-terminal defined in [IMAPABNF].
;; Value 0 denotes that the mailbox doesn't
;; support persistent mod-sequences
;; as described in Section 3.1.2

store-modifier =/ "UNCHANGEDSINCE" SP mod-sequence-valzer
;; Only a single "UNCHANGEDSINCE" may be specified
;; specified in a STORE operation

fetch-modifier =/ chgsince-fetch-mod
;; conforms to the generic "fetch-modifier" syntax
;; syntax defined in [IMAPABNF].

chgsince-fetch-mod = "CHANGEDSINCE" SP mod-sequence-value
;; CHANGEDSINCE FETCH modifier conforms to
;; the fetch-modifier syntax

fetch-att =/ fetch-mod-sequence
;; modifies original IMAP4 fetch-att

fetch-mod-sequence = "MODSEQ"

fetch-mod-resp = "MODSEQ" SP "(" permsg-modsequence ")"

msg-att-dynamic =/ fetch-mod-resp

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search-key =/ search-modsequence
;; modifies original IMAP4 search-key
;;
;; This change applies to all command commands
;; referencing this
;; non-terminal, in
;; particular SEARCH.

search-modsequence = "MODSEQ" [search-modseq-ext] SP
mod-sequence-valzer

search-modseq-ext = SP entry-name SP entry-type-req

resp-text-code =/ "HIGHESTMODSEQ" SP mod-sequence-value /
"NOMODSEQ" /
"MODIFIED" SP set

entry-name = entry-flag-name

entry-flag-name = DQUOTE "/flags/" attr-flag DQUOTE
;; each system or user defined flag <flag>
;; is mapped to "/flags/<flag>".
;;
;; <entry-flag-name> follows the escape rules used
;; used by "quoted" string as described in Section
;; Section 4.3 of [IMAP4], e.g. e.g., for the flag \Seen
;; \Seen the corresponding <entry-name> is
;; "/flags/\\seen", and for the flag
;; $MDNSent, the corresponding <entry-name>
;; is "/flags/$mdnsent".

entry-type-resp = "priv" / "shared"
;; metadata item type

entry-type-req = entry-type-resp / "all"
;; perform SEARCH operation on private
;; metadata item, shared metadata item or both

permsg-modsequence = mod-sequence-value
;; per message mod-sequence

mod-sequence-value = 1*DIGIT
;; Positive unsigned 64-bit integer
;; (mod-sequence)
;; (1 <= n < 18,446,744,073,709,551,615)

mod-sequence-valzer = "0" / mod-sequence-value

search-sort-mod-seq = "(" "MODSEQ" SP mod-sequence-value ")"

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RFC 4551 IMAP Extension for Conditional STORE June 2006

select-param =/ condstore-param
;; conforms to the generic "select-param" non-terminal
;; non-terminal syntax defined in [IMAPABNF].

condstore-param = "CONDSTORE"

mailbox-data =/ "SEARCH" [1*(SP nz-number) SP
search-sort-mod-seq]

attr-flag = "\\Answered" / "\\Flagged" / "\\Deleted" /
"\\Seen" / "\\Draft" / attr-flag-keyword /
attr-flag-extension
;; Does not include "\\Recent"

attr-flag-extension = "\\" atom
;; Future expansion. Client implementations
;; MUST accept flag-extension flags. Server
;; implementations MUST NOT generate
;; flag-extension flags except as defined by
;; future standard or standards-track
;; revisions of [IMAP4].

attr-flag-keyword = atom

5. Server implementation considerations Implementation Considerations

This section describes how a server implementation that doesn't store
separate per-metadata modsequences mod-sequences for different metadata items can
avoid sending the MODIFIED response to any of the following
conditional STORE operations:

+FLAGS
-FLAGS
+FLAGS.SILENT
-FLAGS.SILENT

Note,

Note that the optimization described in this section can't be
performed in case of a conditional STORE FLAGS operation.

Let's use the following example. The client has issued

C: a106 STORE 100:150 (UNCHANGEDSINCE 212030000000)
+FLAGS.SILENT ($Processed)

When the server receives the command and parses it successfully successfully, it
iterates through the message set and tries to execute the conditional
STORE command for each message.

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Each server internally works as a client, i.e. i.e., it has to cache the
current state of all IMAP flags as it is known to the client. In
order to report flag changes to the client client, the server compares the
cached values with the values in its database for IMAP flags.

Imagine that another client has changed the state of a flag \Deleted
on the message 101 and that the change updated the modsequence mod-sequence for
the message. The server knows that the modsequence mod-sequence for the mailbox
has changed, however changed; however, it also knows that that:

a) The the client is not interested in \Deleted flag, as it hasn't
included it in +FLAGS.SILENT operation. operation; and

b) The the state of the flag $Processed hasn't changed (server (the server can
determine this by comparing cached flag state with the state of
the flag in the
database),
so database).

Therefore, the server doesn't have to report MODIFIED to the client. Instead
Instead, the server may set $Processed flag, update the modsequence mod-sequence
for the message 101 once again and send an untagged FETCH response
with new modsequence mod-sequence and flags:

S: * 101 FETCH (MODSEQ (303011130956)
FLAGS ($Processed \Deleted \Answered))

See also section Section 3.8 for additional quality of implementation quality-of-implementation issues.

6. Security Considerations

It is believed that the Conditional STORE extension doesn't raise any
new security concerns that are not already discussed in [IMAP4].
However, the availability of this extension may make it possible for
IMAP4 to be used in critical applications it could not be used for
previously, making correct IMAP server implementation and operation
even more important.

7. IANA Considerations

IMAP4 capabilities are registered by publishing a standards track or
IESG approved experimental RFC. The registry is currently located
at:

http://www.iana.org/assignments/imap4-capabilities

This document defines the CONDSTORE IMAP capability. IANA has added
it to the registry accordingly.

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8. References

7.1.

8.1. Normative References

[KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Harvard University, March 1997.

[ABNF] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 4234, October 2005.

[IMAP4] Crispin, M., "Internet Message Access Protocol "INTERNET MESSAGE ACCESS PROTOCOL - Version VERSION
4rev1", RFC 3501, University of Washington, March 2003.

[IMAPABNF] Melnikov, A., A. and C. Daboo, "Collected extensions Extensions to IMAP4
ABNF",
work in progress.
<http://www.ietf.org/internet-drafts/draft-melnikov-imap-ext-abnf-xx.txt>

7.2. RFC 4466, April 2006.

8.2. Informative References

[ACAP] Newman, C. and J. Myers, "ACAP -- Application
Configuration Access Protocol", RFC 2244, Innosoft, Netscape, November 1997.
<ftp://ftp.isi.edu/in-notes/rfc2244.txt>

[ACL] Melnikov, A., "IMAP4 Access Control List (ACL) Extension",
RFC 4314, December 2005.
<ftp://ftp.isi.edu/in-notes/rfc4314.txt>

[ANN] Daboo, C. and R. Gellens, "IMAP ANNOTATE Extension", Work
in Progress, March 2006.

[NTP] Mills, D, D., "Network Time Protocol (Version 3)
Specification, Implementation and Analysis", RFC 1305,
March 1992.
<ftp://ftp.isi.edu/in-notes/rfc1305.txt>

[RFC-2180] Gahrns, M., "IMAP4 Multi-Accessed Mailbox Practice", RFC
2180, July 1997.
<ftp://ftp.isi.edu/in-notes/rfc2180.txt>

8. IANA Considerations

IMAP4 capabilities are registered by publishing a standards track or
IESG approved experimental RFC. The registry is currently located
at:

http://www.iana.org/assignments/imap4-capabilities

This document defines the CONDSTORE IMAP capability.
IANA should add them to the registry accordingly.

9. Acknowledgments Acknowledgements

Some text was borrowed from "IMAP ANNOTATE Extension" [ANN] by
Randall Gellens and Cyrus Daboo, Daboo and from "ACAP -- Application
Configuration Access Protocol" [ACAP] by Chris Newman and John Myers.

Many thanks to Randall Gellens for his thorough review of the
document.

The authors also acknowledge the feedback provided by Cyrus Daboo,
Larry Greenfield, Chris Newman, Harrie Hazewinkel, Arnt Gulbrandsen,
Timo Sirainen, Mark Crispin, Ned Freed, Ken Murchison Murchison, and Dave
Cridland.

10. Author's

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RFC 4551 IMAP Extension for Conditional STORE June 2006

Authors' Addresses

Alexey Melnikov
mailto: Alexey.Melnikov@isode.com
Isode Limited
5 Castle Business Village, Village
36 Station Road, Road
Hampton, Middlesex, Middlesex
TW12 2BX,
United Kingdom

EMail: Alexey.Melnikov@isode.com

Steve Hole
mailto: Steve.Hole@messagingdirect.com
ACI WorldWide/MessagingDirect

11. Intellectual Property Statement

The IETF takes no position regarding
#1807, 10088 102 Ave
Edmonton, AB
T5J 2Z1
Canada

EMail: Steve.Hole@messagingdirect.com

Melnikov & Hole Standards Track [Page 24]

RFC 4551 IMAP Extension for Conditional STORE June 2006

Full Copyright Statement

This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors
retain all their rights.

This document and the information contained herein are provided on an
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OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
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Acknowledgement

Funding for the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Copyright (C) The Internet Society (2006). This document RFC Editor function is subject
to provided by the rights, licenses and restrictions contained in BCP 78, and
except as set forth therein, the authors retain all their rights.

Acknowledgment

Funding for the RFC Editor function is currently provided by the
Internet Society.

Appendix A. Change History

[[Note to RFC editor: please remove this appendix before publication.]]

0.1. Change History

Changes from draft-ietf-imapext-condstore-08
1. Updated examples not to use time-like modification sequences,
in order not to confuse implementors. (As per comment from
Mark Crispin)
2. Clarified beginning of the second paragraph of section 2,
as per GenArt comment.
3. Updated (informative) reference to ACL RFC.
4. Some other editorial changes to reference [IMAPABNF] content.
5. Repeated and explained the requirement on server implementations
not to bump modification sequence when a flag change operation
results in no flag changes.
6. Explained in Abstract that the CONDSTORE extension can also
be used for quick mailbox resynchronization.

Changes from draft-ietf-imapext-condstore-07
1. Reworded not to have any normative references to SORT.
SORT=MODSEQ has been moved to a separate draft.

Changes from draft-ietf-imapext-condstore-06
1. Minor ABNF update to reference IMAP ABNF properly.

Changes from draft-ietf-imapext-condstore-05
1. Reworded not to have a normative reference to ANNOTATE.
2. Updated ABNF to reference IMAP ABNF.
3. Clarified that STATUS (HIGHESTMODSEQ) also enables
CONDSTORE notifications.
4. Fixed few typos in examples or example titles.
5. Updated boilerplate, references.

Changes from draft-ietf-imapext-condstore-04
1. Fixed typo in an example, added more examples.
2. Clarified client behavior regarding retrying the request
when the server returns MODIFIED (IESG comment)
3. Added new section describing how a CONDSTORE server implementation
should avoid sending MODIFIED when the client has requested
a conditional store on a flag A and a flag B was modified
by another client. (IESG comment)

Changes from draft-ietf-imapext-condstore-03
1. ABNF corrections from Ned Freed.
2. Minor spelling/wording corrections from Ned Freed.

Changes from draft-ietf-imapext-condstore-02
1. Added FETCH modifiers.
2. Added example for using ANNOTATE with UNCHANGEDSINCE STORE
modifier.
3. Added a new requirement to send HIGHESTMODSEQ response code
when implicit enabling is used.
4. Fixed syntax in an example in section 3.2.

Changes from draft-ietf-imapext-condstore-01
1. Fixed missing \\ in one example.
2. Added explanatory comment that search-key modifications apply at
least to SEARCH and SORT command.
3. Don't require from a conditional store operation to be atomic accross
message set, updated text and examples.
4. Added SORT=MODSEQ extension and reworked text in the Introduction section.
5. Added Conditional STORE example based on suggestions from RFC 2180.
6. Removed the paragraph about DOS attack from the Security considerations
section, as it doesn't apply anymore.
7. Updated entry-name ABNF.
8. Added an optional CONDSTORE parameter to SELECT/EXAMINE.

Changes from draft-ietf-imapext-condstore-00
1. Dropped "/message" prefix in entry names as per decision in San Francisco.
2. Fixed ABNF for SEARCH and SORT untagged responses.
3. Changed "private" to "priv" to be consistent with ANNOTATE.
4. MODIFIED response code is now returned in OK response, not NO.
5. Added NOMODSEQ response code.

Changes from draft-melnikov-imap-condstore-09:
1. Some text clarifications based on suggestions by Harrie Hazewinkel
2. Added paragraph about mailbox locking and DOS when conditional STORE
operation is performed on a large mailbox.
3. Fixed syntax of <entry-name> to match the ANNOTATE extension.
4. Added sentence that a system flag MUST always be considered existent,
when UNCHANGEDSINCE 0 is used. Is this a good idea?
5. Clarified client behavior upon receipt of MODIFIED response code.
6. Updated ABNF to clarify where 0 is allowed as mod-sequence and where
it is not.
7. Got rid of MODSEQ response code and return this data in the untagged
SEARCH/SORT responses.
8. Updated RFC number for the IMAP4rev1 document.

Changes from -08 to -09:
1. Added an extended example about reporting regular (non-conditional) flag
changes to other sessions.
2. Simplified FETCH MODSEQ syntax by removing per-metadata requests and
responses.

Changes from -07 to -08:
1. Added note saying the change to UIDVALIDITY also invalidates HIGHESTMODSEQ.
2. Fixed several bugs in ABNF for STATUS and STORE commands.

Changes from -06 to -07:
1. Added clarification that when a server does command reordering, the second
completed operation gets the higher mod sequence.
2. Renamed annotation type specifier "both" to "all" as per suggestion
from Minneapolis meeting.
3. Removed PERFLAGMODSEQ capability, as it doesn't buy anything: a client
has to work with both types of servers (i.e. servers that support per
message per flag modseqs and servers that support only per message
modseqs) anyway.
4. Per flag mod-sequences are optional for a server to return. Updated syntax.
5. Allow MODSEQ response code only as a result of SEARCH/SORT as suggested
by John Myers. MODSEQ response code is not allowed after FETCH or STORE.

Changes from -05 to -06:
1. Replaced "/message/flags/system" with "/message/flags" to
match ANNOTATE draft.
2. Extended FETCH/SEARCH/SORT syntax to allow for specifying
whether an operation should be performed on a shared or a private
annotation (or both).
3. Corrected some examples.

Changes from -04 to -05:
1. Added support for SORT extension.
2. Multiple language/spelling fixes by Randall Gellens.

Changes from -03 to -04:
1. Added text saying that MODSEQ fetch data items cause server
to include MODSEQ data response in all subsuquent unsolicited FETCH
responses.
2. Added "authors address" section.

Changes from -02 to -03:
1. Changed MODTIME untagged response to MODTIME response code.
2. Added MODTIME response code to the tagged OK response for SEARCH.
Updated examples accordingly.
3. Changed rule for sending untagged FETCH response as a result of
STORE when .SILENT prefix is used. If .SILENT prefix is used,
server doesn't have to send untagged FETCH response, because
MODTIME response code already contains modtime.
4. Renamed MODTIME to MODSEQ to make sure there is no confusion
between mod-sequence and ACAP modtime.
5. Minor ABNF changes.
6. Minor language corrections.

Changes from -01 to -02:
1. Added MODTIME data item to STATUS command.
2. Added OK untagged response to SELECT/EXAMINE.
3. Clarified that MODIFIED response code contains list of UIDs for
conditional UID STORE and message set for STORE.
4. Added per-message modtime.
5. Added PERFLAGMODTIME capability.
6. Fixed several bugs in examples.
7. Added more comments to ABNF.

Changes from -00 to -01:
1. Refreshed the list of Open Issues.
2. Changed "attr-name" to "entry-name", because modtime applies to
entry, not attribute.
3. Added MODTIME untagged response.
4. Cleaned up ABNF.
5. Added "Acknowledgments" section.
6. Fixed some spelling mistakes. IETF
Administrative Support Activity (IASA).

Melnikov & Hole Standards Track [Page 25]

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