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draft-ietf-imapext-condstore-01.txt --> draft-ietf-imapext-condstore-02.txt

Document: draft-ietf-imapext-condstore-01.txt draft-ietf-imapext-condstore-02.txt S. Hole
Expires: October December 2003 ACI WorldWide/MessagingDirect
April
June 2003

IMAP Extension for Conditional STORE operation

Status of this Memo

This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026. Internet-Drafts are
working documents of the Internet Engineering Task Force (IETF), its
areas, and its working groups. Note that other groups may also
distribute working documents as Internet-Drafts.

Internet-Drafts are draft documents valid for a maximum of six
months and may be updated, replaced, or obsoleted by other documents
at any time. It is inappropriate to use Internet-Drafts as
reference material or to cite them other than as "work in progress."

The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-
Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.

0.1. Open issues

1). Should conditional STORE be atomic accross message set (i.e. either
all messages in message set weren't changed since and conditional
STORE succeeds or operation fails

Please see the Full Copyright section near the end of this document
for all messages)?
This can be difficult more information.

Abstract

Often, multiple IMAP clients need to implement coordinate changes to a common
IMAP mailbox. Examples include different clients for some servers.

Is the same user,
and multiple users accessing shared mailboxes. These clients
need a server allowed mechanism to reply NO synchronize state changes for messages within the
mailbox. They must be able to a conditional STORE operation guarantee that
contains more than only one message? Do we need client can change
message state (e.g., message flags or annotations) at any time. An
example of such an application is use of an IMAP mailbox as a special response code message
queue with multiple dequeueing clients.

The Conditional Store facility provides a protected update mechanism for this (probably yes).

0.2. Change History
message state information that can detect and resolve conflicts between
multiple writing mail clients.

Table of Contents

1 Conventions Used in This Document ......................... X
2 Introduction and Overview ................................. X
3 IMAP Protocol Changes from draft-ietf-imapext-condstore-00
1. Dropped "/message" prefix ..................................... X
3.1 New OK untagged responses for SELECT and EXAMINE ......... X
3.1.1 HIGHESTMODSEQ response code ............................ X
3.1.2 NOMODSEQ response code ................................. X
3.2 STORE and UID STORE Commands ............................. X
3.3 MODSEQ message data item in entry names as per decision FETCH Command ................ X
3.4 MODSEQ search criterion in San Francisco.
2. Fixed ABNF for SEARCH ........................ X
3.5 MODSEQ Sort Criterion .................................... X
3.6 Modified SEARCH and SORT untagged responses.
3. Changed "private" responses .............. X
3.7 HIGHESTMODSEQ status data items .......................... X
3.8 CONDSTORE parameter to "priv" SELECT and EXAMINE ................ X
4 Formal Syntax ............................................. X
5 Security Considerations ................................... X
6 References ................................................ X
6.1 Normative References ..................................... X
6.2 Informative References ................................... X
7 IANA Considerations ....................................... X
8 Acknowledgments ........................................... X
9 Author's Addresses ........................................ X
10 Intellectual Property Rights .............................. X
11 Full Copyright Statement .................................. X

1. 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 consistent with ANNOTATE.
4. MODIFIED response code is now returned interpreted as described in OK response, not NO.
5. Added NOMODSEQ response code.

Changes from draft-melnikov-imap-condstore-09:
1. Some text clarifications based on suggestions RFC 2119 [KEYWORDS].

In examples, lines beginning with "S:" are sent by Harrie Hazewinkel
2. Added paragraph about mailbox locking the IMAP server, and DOS when conditional STORE
operation is performed on a large mailbox.
3. Fixed syntax of <entry-name> to match
lines beginning with "C:" are sent by the ANNOTATE extention.
4. Added sentence that a system flag MUST always be considered existent, client. Line breaks may appear
in example commands solely for editorial clarity; when UNCHANGEDSINCE 0 present in
the actual message they are represented by "CRLF".

Formal syntax is used. Is this a good idea?
5. Clarified client behavior upon receipt of MODIFIED response code.
6. Updated defined using ABNF to clarify where 0 is allowed [ABNF] as mod-sequence and where
it modified by [IMAP4].

The term "metadata" or "metadata item" is not.
7. Got rid of MODSEQ response code and return used throughout this data in the untagged
SEARCH/SORT responses.
8. Updated RFC number for the IMAP4rev1 document.

Changes from -08
It refers to -09:
1. Added any system or user defined keyword or an extended example about reporting regular (non-conditional) flag
changes annotation
[ANNOTATE].

Some IMAP mailboxes are private, accessible only to other sessions.
2. Simplified FETCH MODSEQ syntax the owning user.
Other mailboxes are not, either because the owner has set an ACL
[ACL] which permits access by removing per-metadata requests and
responses.

Changes from -07 to -08:
1. Added note saying other users, or because it is a
shared mailbox. Let's call a metadata item "shared" for the change mailbox
if any changes to UIDVALIDITY also invalidates HIGHESTMODSEQ.
2. Fixed several bugs in ABNF for STATUS the metadata items are persistent and STORE commands.

Changes from -06 visible to -07:
1. Added clarification that when a server does command reordering, all
other users accessing the second
completed operation gets mailbox. Otherwise the higher mod sequence.
2. Renamed annotation type specifier "both" metadata item is called
"private". Note, that private metadata items are still visible to "all" as per suggestion
from Minneapolis meeting.
3. Removed PERFLAGMODSEQ capability, all
sessions accessing the mailbox 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 the same user. Also note, that support only per message
modseqs) anyway.
4. Per flag mod-sequences are optional different
mailboxes may have different metadata items as shared.

See the next section for the definition of a server to return. Updated syntax.
5. Allow MODSEQ response code only as "CONDSTORE-aware client"
and 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. "CONDSTORE enabling command".

2. Extended FETCH/SEARCH/SORT syntax to allow for specifying
whether Introduction and Overview

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

Every IMAP message has an operation should be performed on associated positive unsigned 64-bit value called a shared or
modification sequence (mod-sequence). This is an opaque value updated by
the server whenever a private
annotation (or both).
3. Corrected some examples.

Changes from -04 metadata item is modified. The value is intended to -05:
1. Added support
be used only 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 comparisons within a server. However, the server MUST
guarantee that each STORE command performed on the same mailbox, including
simultaneous stores to include MODSEQ data response in all subsuquent unsolicited FETCH
responses.
2. Added "authors address" section.

Changes different metadata items 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 different connections,
will get a result of different mod-sequence value. Also, for any two successful
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 operations performed in the same session on the same mailbox,
the 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 second completed operation MUST be greater than
the mod-sequence of Open Issues.
2. Changed "attr-name" to "entry-name", the first completed. Note that the latter rule disallows
the use of the system clock as a mod-sequence, because modtime applies if system time changes
(e.g., a 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
entry, not attribute.
3. Added MODTIME untagged response.
4. Cleaned up ABNF.
5. Added "Acknowledgments" section.
6. Fixed
determine if a message metadata has changed since some spelling mistakes.

Table known
moment. Whenever the state of Contents

1 Abstract .................................................. X
2 Conventions Used in This Document ......................... X
3 Introduction a flag changes (i.e., the flag is added and Overview ................................. X
4 IMAP Protocol Changes ..................................... X
4.1 New OK untagged responses for SELECT
before it wasn't set, or the flag is removed and EXAMINE ......... X
4.1.1 HIGHESTMODSEQ response code ............................ X
4.1.2 NOMODSEQ response code ................................. X
4.2 STORE and UID STORE Commands ............................. X
4.3 MODSEQ message data item in FETCH Command ................ X
4.4 MODSEQ search criterion in SEARCH ........................ X
4.5 MODSEQ Sort Criterion .................................... X
4.6 Modified SEARCH and SORT untagged responses .............. X
4.7 HIGHESTMODSEQ status data items .......................... X
5 Formal Syntax ............................................. X
6 Security Considerations ................................... X
7 References ................................................ X
7.1 Normative References ..................................... X
7.2 Informative References ................................... X
8 Acknowledgments ........................................... X
9 Author's Addresses ........................................ X
10 Full Copyright Statement ................................. X

1. Abstract

Often, multiple IMAP clients need to coordinate changes to a common
IMAP mailbox. Examples include different clients for before it was set) the same user,
and multiple users accessing shared mailboxes. These clients
need a mechanism to synchronize state changes
value of the modification sequence for messages within the
mailbox. They must message MUST be able to guarantee that only one client can 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 state (e.g., message flags is appended to a mailbox (via the IMAP APPEND command,
COPY to the mailbox or annotations) at any time. An
example of such using an application external mechanism) the server
generates a new modification sequence that is use higher than the highest
modification sequence of an IMAP all messages in the mailbox as a and assigns it to
the appended message.

When an annotation is added, modified or removed the corresponding message
queue with multiple dequeueing clients.
mod-sequence MUST be updated.

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

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 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 server MAY store separate (per message) modification sequence values for editorial clarity; when present in
different metadata items. If the actual server does so, per message they are represented by "CRLF".

Formal syntax mod-sequence is defined using ABNF [ABNF] as modified by [IMAP4].
the highest mod-sequence of all metadata items for the specified message.

The term "metadata" or "metadata item" is used throughout server that supports this document.
It refers extention is not required to any system or user defined keyword or an annotation
[ANNOTATE].

Some IMAP mailboxes are private, accessible only be able 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" store
mod-sequences for every available mailbox. Section 3.1.2 describes how
the mailbox server may act if any changes to a particular mailbox doesn't support the metadata items are persistent and visible
storage of mod-sequences.

This extension makes the following changes to all
other users accessing the mailbox. Otherwise IMAP4 protocol:

a) extends 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.

3. Introduction and Overview

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

Every IMAP message has an associated positive unsigned 64-bit value called a
modification sequence (mod-sequence). This is an opaque value updated by
the server whenever a metadata item is modified. The value is intended to allow STORE
modifiers

b) adds the MODIFIED response code which should be used only for comparisons within a server. However, with
an OK response to the server MUST
guarantee that each STORE command performed on the same mailbox, including
simultaneous stores to different metadata items from different connections,
will get

c) adds a different mod-sequence value. Also, new MODSEQ message data item for any two successful
STORE operations performed in the same session on use with the same mailbox, FETCH command

d) adds a new MODSEQ search criterion

e) extends the mod-sequence syntax of the second completed operation MUST be greater than
the untagged SEARCH responses to include 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 NTP [NTP] client adjusting

f) adds new OK untagged responses for the time), SELECT and EXAMINE commands

g) defines an additional parameter to SELECT/EXAMINE commands

h) adds the next generated value might
be less than HIGHESTMODSEQ status data item to the previous one.

Mod-sequences allow a STATUS command

A client that supports the supporting CONDSTORE extension indicates its willingness to
determine if receive
mod-sequence updates in all untagged FETCH responses by issuing a message metadata has changed since some known
moment. Whenever SELECT or
EXAMINE command with the state of CONDSTORE parameter, or a flag changes (i.e., the flag is added and
before it wasn't set, FETCH, SEARCH, or the flag is removed and before SORT
(if it was set) the
value of the modification sequence for also supports SORT=MODSEQ extension, see below) command that includes
the MODSEQ message MUST be updated.
Adding the flag when it is already present data item, or removing when it is not
present SHOULD NOT change a STORE command with the mod-sequence.

When UNCHANGEDSINCE modifier.
The server will include mod-sequence data in all FETCH responses, whether they
were caused by a message regular STORE, STORE with UNCHANGEDSINCE modifier, or an external
agent, until the connection is appended closed.

This document uses the term "CONSTORE-aware client" to refer to a mailbox (via the IMAP APPEND command,
COPY client
that announces its willingness to receive mod-sequence updates as described
above. The term "CONDSTORE enabling command" will refer any of the mailbox or using an external mechanism) the server
generates commands
listed above.

This document also defines a new modification sequence that SORT extension with a capability name
"SORT=MODSEQ". This extension is higher than upwards compatible with the highest
modification sequence of all messages SORT extension
defined in [SORT]. Server implementations that support both the mailbox CONDSTORE and assigns it to
the appended message.

When an annotation is added, modified or removed
SORT extensions SHOULD also support the corresponding message
mod-sequence MUST be updated. SORT=MODSEQ extension. The server MAY store separate (per message) modification sequence values for
different metadata items. If
SORT=MODSEQ extension makes the server does so, per message mod-sequence is following additions to the highest mod-sequence of all metadata items for the specified message.

The server that supports this extention is not required to be able to store
mod-sequences for every available mailbox. Section 4.1.2 describes how
the server may act if a particular mailbox doesn't support the persistent
storage of mod-sequences.

This extension makes the following changes to the IMAP4 protocol:

a) extends the syntax of the STORE command to allow STORE
modifiers

b) adds the MODIFIED response code which should be used with
an OK response to the STORE command

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

d) adds a new MODSEQ search criterion

e) extends syntax SORT extension:

a) extends syntax of untagged SEARCH and SORT responses to include
mod-sequence.

f) adds a new OK untagged responses for the SELECT and EXAMINE commands

g) adds the HIGHESTMODSEQ status data item to the STATUS command

h) mod-sequence
(see section 3.6)

b) adds a new MODSEQ sort criterion (see sections 3.4 and 3.5)

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

3. IMAP Protocol Changes

4.1.

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 and EXAMINE commands.

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 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.

4.1.1.

3.1.1. HIGHESTMODSEQ 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 <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 flags and/or annotations 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 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 4.4 3.4 to find out exactly
which metadata items have changed.

Example: 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 [HIGHESTMODSEQ 20010715194045007]
S: A142 OK [READ-WRITE] SELECT completed

4.1.2

3.1.2 NOMODSEQ 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: 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

4.2.

3.2. STORE and UID STORE Commands

Arguments: message set
OPTIONAL store modifiers
message data item name
value for message data item

Responses: untagged responses: FETCH

Result: OK - store completed
NO - store error: can't store that data
BAD - command unknown or arguments invalid

This document extends the syntax of the STORE and UID STORE
commands (see section 6.4.6 of [IMAP4]) to include an optional STORE
modifier. The document defines the following modifier:

UNCHANGEDSINCE
For each message specified in the message set the server performs
the following. If the mod-sequence of any metadata item specified in the STORE
operation for any message in of the
message set is greater equal or less than the specified unchangedsince UNCHANGEDSINCE value,
then the command MUST NOT change
any flags. Instead, requested operation (as described by the
message data item) is performed. If the operation is successful
the server replies with MUST update the OK tagged response that
includes a MODIFIED mod-sequence attribute of the message.
An untagged FETCH response code. The MODIFIED MUST be sent (even if the .SILENT suffix
is specified) and the response code includes MUST include the MODSEQ message set (for STORE) or set data
item. This is required to update the client's cache with the correct
mod-sequence values. See section 3.3 for more details.

However, if the mod-sequence of UIDs (for UID STORE) any metadata item of all messages that failed the UNCHANGESINCE test.

Example:

C: a101
message is greater than the specified UNCHANGEDSINCE value, than
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 7,5,9
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 :

All messages pass the UNCHANGESINCE test.

C: a103 UID STORE 6,4,8 (UNCHANGEDSINCE 20000320162338) 200012121230045)
+FLAGS.SILENT (\Deleted)
S: a101 * 1 FETCH (UID 4 MODSEQ (200012121231000))
S: * 2 FETCH (UID 6 MODSEQ (200012101230852))
S: * 4 FETCH (UID 8 MODSEQ (200012121130956))
S: a103 OK [MODIFIED 7,9] Conditional Store completed

Example:

C: a104 STORE failed * (UNCHANGEDSINCE 200012121230045) +FLAGS.SILENT
(\Deleted $Processed)
S: * 50 FETCH (MODSEQ (200012111230045))
S: a104 OK Store (conditional) completed

Example:

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 fail the test.

C: a105 STORE 7,5,9 (UNCHANGEDSINCE 20000320162338)
+FLAGS.SILENT (\Deleted)
S: * 5 FETCH (MODSEQ (20000320162350))
S: a105 OK [MODIFIED 7,9] Conditional STORE failed

Example:

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

C: a105 STORE 7,5,9 (UNCHANGEDSINCE 20000320162338)
+FLAGS.SILENT (\Deleted)
S: * 7 FETCH (MODSEQ (20000320162342) FLAGS (\Seen \Deleted))
S: * 5 FETCH (MODSEQ (20000320162350))
S: * 9 FETCH (MODSEQ (20000320162349) FLAGS (\Answered))
S: a105 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:

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

Note: A client trying to atomically make an atomic change to the state of a particular
flag
metadata item (or a set of flags) metadata items) should be prepared
to deal with the case when the server returns MODIFIED response code
if the state of the flag metadata item being watched hasn't changed (but
the state of some other flag metadata item has). This is necessary, because
some servers don't store separate mod-sequences for different flags or annotations. metadata
items. However, a server implementations are discouraged from doing that, as it is
possible not to return implementation SHOULD avoid generating
spurious errors MODIFIED responses for +FLAGS/-FLAGS STORE operations,
even when storing the server stores a single mod-sequence per message.

Upon the receipt of MODIFIED response code the client SHOULD try to
figure out if the required flags metadata items have indeed changed. If they
haven't the client SHOULD retry the command.

Example:
C: a106 STORE 100:150 (UNCHANGEDSINCE 200212030000000)
+FLAGS.SILENT ($Processed)
S: * 100 FETCH (MODSEQ (200303181230852))
S: * 102 FETCH (MODSEQ (200303181230852))
...
S: * 150 FETCH (MODSEQ (200303181230852))
S: a106 OK [MODIFIED 101] Conditional STORE failed

the flag $Processed was set on the message 101 ...
C: a107 NOOP
S: * 101 FETCH (MODSEQ (200303011130956) FLAGS ($Processed))
S: a107 OK

... so the client retries the operation for the rest of the messages

C: a108 STORE 100,102:150 (UNCHANGEDSINCE 200303011130956)
+FLAGS.SILENT ($Processed)
S: * 100 FETCH (MODSEQ (200303181230852))
S: * 102 FETCH (MODSEQ (200303181230852))
...
S: a108 OK Conditional Store completed

Or the flag hasn't changed ...
C: b107 NOOP
S: * 101 FETCH (MODSEQ (200303011130956) FLAGS (\Deleted \Answered))
S: b107 OK

... and the client retries the operation for all messages the message 100
with the updated UNCHANGEDSINCE value

C: b108 STORE 100:150 100 (UNCHANGEDSINCE 200212030000000) 200303011130956)
+FLAGS.SILENT ($Processed)
S: * 100 FETCH (MODSEQ (200303181230852))
S: * 101 FETCH (MODSEQ (200303181230852))
S: * 102 FETCH (MODSEQ (200303181230852))
...
S: b108 OK Conditional Store completed

If the operation

Example:

The following example is successful based on the server MUST update example from the
mod-sequence attribute for every message section 4.2.3 of
[RFC-2180] and demonstrates that was changed.
Untagged FETCH responses MUST the MODIFIED response code may be sent (even if .SILENT is
specified) also
returned in the tagged NO response.

Client tries to conditionally STORE flags on a mixture of expunged
and each response MUST include MODSEQ non-expunged messages, one message data
item if its mod-sequence has changed. This is required to
update clients cache with fails the correct mod-sequence values.
See section 4.3 for more details.

Example: UNCHANGEDSINCE test.

C: a103 UID B001 STORE 6,4,8 1:7 (UNCHANGEDSINCE 200012121230045)
+FLAGS.SILENT (\Deleted) 20000320172338) +FLAGS (\SEEN)
S: * 1 FETCH (UID 4 MODSEQ (200012121231000)) FLAGS (MODSEQ (20000320172342) \SEEN)
S: * 2 3 FETCH (UID 6 MODSEQ (200012101230852)) FLAGS (MODSEQ (20000320172342) \SEEN)
S: B001 NO [MODIFIED 2] Some of the messages no longer exist.

C: B002 NOOP
S: * 4 FETCH (UID 8 MODSEQ (200012121130956)) EXPUNGE
S: a103 OK Conditional Store completed

Example:

C: a104 STORE * (UNCHANGEDSINCE 200012121230045) +FLAGS.SILENT
(\Deleted $Processed) 4 EXPUNGE
S: * 50 4 EXPUNGE
S: * 4 EXPUNGE
S: * 2 FETCH (MODSEQ (200012111230045)) (20000320172340) FLAGS (\Deleted \Answered))
S: a104 B002 OK NOOP Completed.

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

C: b003 STORE 2 (UNCHANGEDSINCE 20000320172340) +FLAGS (\Seen)
S: * 2 FETCH (MODSEQ (20000320180050))
S: b003 OK Conditional Store (conditional) 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:

a105 STORE 7,3:9 (UNCHANGEDSINCE 200012121230045)
+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.

4.3.

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.

3.3. MODSEQ 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 4.2) 3.2) and/or
changes caused by external sources.

Example:

C: a FETCH 1:3 (MODSEQ)
S: * 1 FETCH (MODSEQ (20000624140003))
S: * 2 FETCH (MODSEQ (20000624140007))
S: * 3 FETCH (MODSEQ (20000624140005))
S: a OK Fetch complete

In this example the client requests 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 for the
message.

Example:

(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
...

C: A160 STORE 7 +FLAGS.SILENT (\Deleted)
S: * 7 FETCH (MODSEQ (200012121231000))
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 (200012121231000))
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 (200012121231000))
S: D210 OK Noop completed

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

C: A240 STORE 7 +FLAGS.SILENT (\Seen)
S: * 7 FETCH (MODSEQ (200012121231777))
S: A240 OK Store completed

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

C: C270 NOOP
S: * 7 FETCH (FLAGS (\Deleted \Answered \Seen) MODSEQ (200012121231777))
S: C270 OK Noop completed

... but not in the session 3.

C: D300 NOOP
S: D300 OK Noop completed

And 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 (200012121245160))
S: A330 OK Store completed

Both changes are reported in the session 2 ...

C: C360 NOOP
S: * 7 FETCH (FLAGS (\Deleted) MODSEQ (200012121245160))
S: C360 OK Noop completed

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

C: D390 NOOP
S: * 7 FETCH (FLAGS (\Deleted) MODSEQ (200012121245160))
S: D390 OK Noop completed

4.4.

3.4. MODSEQ 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 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) or "all". The latter means that the server should use
the biggest value among "priv" and "shared" mod-sequences for the
metadata item. If the server doesn't store internally separate
mod-sequences for different flags and annotations, metadata items, it MUST ignore
<entry-name> and <entry-type-req>. Otherwise the server should
use them to narrow down the search.

For a flag <flagname> the corresponding <entry-name> has a form
"/flags/<flagname>" as defined in [ANNOTATE]. 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
return a MODSEQ response code in
append (to the tagged OK response. The MODSEQ
response code covers all messages returned in end of the untagged SEARCH results. response) the highest
mod-sequence for all messages being returned. See also section 4.6. 3.6.

Example:
C: a SEARCH MODSEQ "/flags/draft" "/flags/\\draft" all 20010320162338
ANNOTATION "/comment" "value" "IMAP4"
S: * SEARCH 2 5 6 7 11 12 18 19 20 23 (MODSEQ 20010917162500)
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 20010320162338 for the "\Draft" flag are returned in
the search results.

Example:
C: a SEARCH OR NOT MODSEQ 20010320162338 LARGER 50000
S: * SEARCH
S: a OK Search complete, nothing found

4.5.

3.5. MODSEQ Sort Criterion

If a server implementing CONDSTORE also implements the SORT
extension as defined by [SORT], it MUST also support SHOULD implement the
SORT=MODSEQ extension that allows for sorting on per-message
mod-sequence.

Syntax: SORT=MODSEQ extension adds MODSEQ sort criterion
that allows to sort the matching messages based on their mod-sequence.

If client specifies a MODSEQ search (as per section 4.4) 3.4) or sort
criterion in the SORT command and the server returns a non-empty
SORT result, the server MUST also return a MODSEQ response
code in append (to the end of the tagged OK response which covers all messages returned
in untagged
SORT responses. response) the highest mod-sequence for all messages being returned.
See also section 4.6.

Example: 3.6.

Example (MODSEQ search criterion):

C: A282 SORT (SUBJECT MODSEQ) UTF-8 SINCE 1-Feb-2001
S: * SORT 2 81 83 84 82 882 (MODSEQ 117)
S: A282 OK SORT completed

Example:

Example (MODSEQ sort criterion):

C: A283 SORT (SUBJECT REVERSE DATE) UTF-8 MODSEQ 21
S: * SORT 6 3 4 5 2 (MODSEQ 125)
S: A283 OK SORT completed

Example:

Example (MODSEQ search criterion and MODSEQ SORT criterion,
but no messages matching the search criteria):

C: A284 SORT (MODSEQ) KOI8-R OR NOT MODSEQ 20010320162338
SUBJECT "Privet"
S: * SORT
S: A284 OK Sort complete, nothing found

4.6.

3.6. Modified SEARCH and SORT untagged responses

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

This document extends syntax of the untagged SEARCH and SORT responses
to include 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
3.4 for examples.

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

4.7. See section
3.5 for examples.

3.7. HIGHESTMODSEQ status data items

This document defines a new status data item:

HIGHESTMODSEQ
The highest mod-sequence value all messages
in the mailbox. This is the same value that is returned by the server
in the HIGHESTMODSEQ response code in OK untagged response
(see section 4.1.1). 3.1.1).

Example: C: A042 STATUS blurdybloop (UIDNEXT MESSAGES HIGHESTMODSEQ)
S: * STATUS blurdybloop (MESSAGES 231 UIDNEXT 44292
HIGHESTMODSEQ 200201011231777)
S: A042 OK STATUS completed

5. Formal Syntax

3.8. CONDSTORE parameter to SELECT and EXAMINE

The CONDSTORE extension defines a single optional select 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 metadata item(s) is(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: 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 20010715194045007]
S: A142 OK [READ-WRITE] SELECT completed, CONDSTORE is now enabled

4. Formal Syntax

The following syntax specification uses the Augmented Backus-Naur
Form (ABNF) notation as specified in [ABNF].

Non-terminals referenced but not defined below are as defined by
[IMAP4].

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.

capability =/ "CONDSTORE" / "SORT=MODSEQ"

status = "STATUS" SP mailbox SP
"(" status-att-req *(SP status-att-req) ")"
;; redefine STATUS command syntax defined in [IMAP4]

status-att-req = status-att / "HIGHESTMODSEQ"

status-rsp-info = status-att SP number /
"HIGHESTMODSEQ" SP mod-sequence-value

store = "STORE" SP set store-modifiers SP store-att-flags

store-modifiers = [ SP "(" store-modifier *(SP store-modifier) ")" ]

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

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

fetch-mod-sequence = "MODSEQ"

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

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

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-name-flag / entry-annotate-name
;; The server MUST understand entry-name-flag.
;; If the server also supports [ANNOTATE], it MUST
;; also support entry-annotate-name.

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

entry-annotate-name = entry
;; <entry> is defined in [ANNOTATE]

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 ")"

sort-key =/ "MODSEQ"

condstore-param = "CONDSTORE"
;; defines the select parameter used with
;; CONDSTORE extension

;;Borrowed from IMAP4rev1 and modified accordingly:

mailbox-data =/ "STATUS" SP mailbox SP "("
[status-rsp-info *(SP status-rsp-info)] ")" /
"SEARCH" [1*(SP nz-number) SP search_sort_mod_seq] /
"SORT" [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" "\\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 this specification. [IMAP4].

attr-flag-keyword = atom

5. Security Considerations

As a conditional STORE operation must be atomic for a message set,
an implementation may choose to use some kind of message or even
mailbox level locking for the duration of

It is believed that the conditional STORE
operation. Such implementation may suffer from a Deny of Service
Attack when conditional Conditional STORE is executed on a large mailbox.

Other IMAP4 extension doesn't raise
any new security issues can be found concerns that are not already discussed in Security Considerations
section of [IMAP4].

6. References

7.1.

6.1. Normative References

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

[ABNF] Crocker, Overell, "Augmented BNF for Syntax Specifications:
ABNF", RFC 2234, Internet Mail Consortium, Demon Internet Ltd,
November 1997.

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

[ANNOTATE] Gellens, R., Daboo, C., "IMAP ANNOTATE Extension",
work in progress.
<http://www.ietf.org/internet-drafts/draft-ietf-imapext-annotate-xx.txt>

[SORT] Crispin, M., Murchison, K., "Internet Message Access Protocol --
SORT
Extension", AND THREAD EXTENSIONS", work in progress.
<http://www.ietf.org/internet-drafts/draft-crispin-imapext-sort-xx.txt>

7.2.
<http://www.ietf.org/internet-drafts/draft-ietf-imapext-sort-xx.txt>

6.2. Informative References

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

[ACL] Myers, "IMAP4 ACL extension", RFC 2086, Carnegie Mellon,
January 1997.
<ftp://ftp.isi.edu/in-notes/rfc2086.txt>

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

8. Acknowledgments

Some

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

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 consitutes registration of the CONDSTORE and SORT=MODSEQ
IMAP capabilities.

8. Acknowledgments

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

Many thanks to Randall Gellens for his comments on how CONDSTORE should
interact with ANNOTATE extension and for thorough review of the document.

Authors also acknowledge the feedback provided by Cyrus Daboo, Larry
Greenfield, Chris Newman, Harrie Hazewinkel, Arnt Gulbrandsen Gulbrandsen, Timo
Sirainen and Mark Crispin.

9. Author's Addresses

Alexey Melnikov
mailto: mel@messagingdirect.com

ACI WorldWide/MessagingDirect
59 Clarendon Road, Watford, Hertfordshire,
WD17 1FQ, United Kingdom mel@isode.com

Isode Limited

Steve Hole
mailto: Steve.Hole@messagingdirect.com

ACI WorldWide/MessagingDirect
#900, 10117 Jasper Avenue,
Edmonton, Alberta, T5J 1W8, CANADA

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Appendix A. Open Issues and Change History

Note that this appendix will be removed before publication.

0.1. Change History

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 extention.
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 -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.
----