< draft-ietf-imapext-sort-19.txt   draft-ietf-imapext-sort-20.txt >
IMAP Extensions Working Group M. Crispin IMAP Extensions Working Group M. Crispin
Internet-Draft K. Murchison Internet-Draft K. Murchison
Intended status: Proposed Standard September 5, 2007 Intended status: Proposed Standard March 10, 2008
Expires: March 5, 2008 Expires: September 10, 2008
Document: internet-drafts/draft-ietf-imapext-sort-19.txt Document: internet-drafts/draft-ietf-imapext-sort-20.txt
INTERNET MESSAGE ACCESS PROTOCOL - SORT AND THREAD EXTENSIONS INTERNET MESSAGE ACCESS PROTOCOL - SORT AND THREAD EXTENSIONS
Status of this Memo Status of this Memo
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Abstract Abstract
This document describes the base-level server-based sorting and This document describes the base-level server-based sorting and
threading extensions to the [IMAP] protocol. These extensions threading extensions to the [IMAP] protocol. These extensions
provide substantial performance improvements for IMAP clients which provide substantial performance improvements for IMAP clients which
offer sorted and threaded views. offer sorted and threaded views.
1. Introduction 1. Introduction
The SORT and THREAD extensions to the [IMAP] protocol provide a means The SORT and THREAD extensions to the [IMAP] protocol provide a means
of server-based sorting and threading of messages, without requiring of server-based sorting and threading of messages, without requiring
that the client download the necessary data to do so itself. This is that the client download the necessary data to do so itself. This is
particularly useful for online clients as described in [IMAP-MODELS]. particularly useful for online clients as described in [IMAP-MODELS].
A server which supports the base-level SORT extension indicates this A server which supports the base-level SORT extension indicates this
with a capability name which starts with "SORT". Future, with a capability name which starts with "SORT". Future,
upwards-compatible extensions to the SORT extension will all start upwards-compatible extensions to the SORT extension will all start
with "SORT", indicating support for this base level. with "SORT", indicating support for this base level.
A server which supports the THREAD extension indicates this with one A server which supports the THREAD extension indicates this with one
or more capability names consisting of "THREAD=" followed by a or more capability names consisting of "THREAD=" followed by a
supported threading algorithm name as described in this document. supported threading algorithm name as described in this document.
This provides for future upwards-compatible extensions. This provides for future upwards-compatible extensions.
A server which implements the SORT and/or THREAD extensions SHOULD A server which implements the SORT and/or THREAD extensions MUST
also implement the COMPARATOR extension as described in [IMAP-I18N]. collate strings in accordance with the requirements of I18NLEVEL=1,
as described in [IMAP-I18N], and SHOULD implement and advertise the
I18NLEVEL=1 extension. Alternatively, a server MAY implement
I18NLEVEL=2 (or higher) and comply with the rules of that level.
Discussion: the SORT and THREAD extensions predate [IMAP-I18N] by
several years. At the time of this writing, all known server
implementations of SORT and THREAD comply with the rules of
I18NLEVEL=1, but do not necessarily advertise it. As discussed
in [IMAP-I18N] section 4.5, all server implementations should
eventually be updated to comply with the I18NLEVEL=2 extension.
Historical note: the REFERENCES threading algorithm is based on the
[THREADING] algorithm written used in "Netscape Mail and News"
versions 2.0 through 3.0.
2. Terminology 2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [KEYWORDS]. document are to be interpreted as described in [KEYWORDS].
The word "can" (not "may") is used to refer to a possible The word "can" (not "may") is used to refer to a possible
circumstance or situation, as opposed to an optional facility of the circumstance or situation, as opposed to an optional facility of the
protocol. protocol.
"User" is used to refer to a human user, whereas "client" refers to "User" is used to refer to a human user, whereas "client" refers to
the software being run by the user. the software being run by the user.
In examples, "C:" and "S:" indicate lines sent by the client and In examples, "C:" and "S:" indicate lines sent by the client and
server respectively. server respectively.
2.1 Base Subject 2.1 Base Subject
Subject sorting and threading use the "base subject," which has Subject sorting and threading use the "base subject," which has
specific subject artifacts removed. Due to the complexity of these specific subject artifacts removed. Due to the complexity of these
artifacts, the formal syntax for the subject extraction rules is artifacts, the formal syntax for the subject extraction rules is
ambiguous. The following procedure is followed to determine the ambiguous. The following procedure is followed to determine the
"base subject", using the [ABNF] formal syntax rules described in "base subject", using the [ABNF] formal syntax rules described in
section 5: section 5:
(1) Convert any RFC 2047 encoded-words in the subject to (1) Convert any RFC 2047 encoded-words in the subject to
UTF-8 as described in "internationalization UTF-8 as described in "internationalization
considerations." Convert all tabs and continuations to considerations." Convert all tabs and continuations to
space. Convert all multiple spaces to a single space. space. Convert all multiple spaces to a single space.
(2) Remove all trailing text of the subject that matches (2) Remove all trailing text of the subject that matches
the subj-trailer ABNF, repeat until no more matches are the subj-trailer ABNF, repeat until no more matches are
possible. possible.
(3) Remove all prefix text of the subject that matches the (3) Remove all prefix text of the subject that matches the
subj-leader ABNF. subj-leader ABNF.
(4) If there is prefix text of the subject that matches the (4) If there is prefix text of the subject that matches the
subj-blob ABNF, and removing that prefix leaves a non-empty subj-blob ABNF, and removing that prefix leaves a non-empty
subj-base, then remove the prefix text. subj-base, then remove the prefix text.
(5) Repeat (3) and (4) until no matches remain. (5) Repeat (3) and (4) until no matches remain.
Note: it is possible to defer step (2) until step (6), but this Note: it is possible to defer step (2) until step (6), but this
requires checking for subj-trailer in step (4). requires checking for subj-trailer in step (4).
(6) If the resulting text begins with the subj-fwd-hdr ABNF (6) If the resulting text begins with the subj-fwd-hdr ABNF
and ends with the subj-fwd-trl ABNF, remove the and ends with the subj-fwd-trl ABNF, remove the
subj-fwd-hdr and subj-fwd-trl and repeat from step (2). subj-fwd-hdr and subj-fwd-trl and repeat from step (2).
(7) The resulting text is the "base subject" used in the (7) The resulting text is the "base subject" used in the
SORT. SORT.
All servers and disconnected (as described in [IMAP-MODELS]) clients All servers and disconnected (as described in [IMAP-MODELS]) clients
MUST use exactly this algorithm to determine the "base subject". MUST use exactly this algorithm to determine the "base subject".
Otherwise there is potential for a user to get inconsistent results Otherwise there is potential for a user to get inconsistent results
based on whether they are running in connected or disconnected mode. based on whether they are running in connected or disconnected mode.
2.2 Sent Date 2.2 Sent Date
As used in this document, the term "sent date" refers to the date and As used in this document, the term "sent date" refers to the date and
time from the Date: header, adjusted by time zone to normalize to time from the Date: header, adjusted by time zone to normalize to
UTC. For example, "31 Dec 2000 16:01:33 -0800" is equivalent to the UTC. For example, "31 Dec 2000 16:01:33 -0800" is equivalent to the
UTC date and time of "1 Jan 2001 00:01:33 +0000". UTC date and time of "1 Jan 2001 00:01:33 +0000".
If the time zone is invalid, the date and time SHOULD be treated as If the time zone is invalid, the date and time SHOULD be treated as
UTC. If the time is also invalid, the time SHOULD be treated as UTC. If the time is also invalid, the time SHOULD be treated as
00:00:00. If there is no valid date or time, the date and time 00:00:00. If there is no valid date or time, the date and time
SHOULD be treated as 00:00:00 on the earliest possible date. SHOULD be treated as 00:00:00 on the earliest possible date.
This differs from the date-related criteria in the SEARCH command This differs from the date-related criteria in the SEARCH command
(described in [IMAP] section 6.4.4), which use just the date and not (described in [IMAP] section 6.4.4), which use just the date and not
the time, and are not adjusted by time zone. the time, and are not adjusted by time zone.
If the sent date can not be determined (a Date: header is missing or
can not be parsed), the INTERNALDATE for that message is used as the
sent date.
When comparing two sent dates that match exactly, the order in which
the two messages appear in the mailbox (that is, by sequence number)
is used as a tie-breaker to determine the order.
3. Additional Commands 3. Additional Commands
These commands are extension to the [IMAP] base protocol. These commands are extension to the [IMAP] base protocol.
The section headings are intended to correspond with where they would The section headings are intended to correspond with where they would
be located in the main document if they were part of the base be located in the main document if they were part of the base
specification. specification.
BASE.6.4.SORT. SORT Command BASE.6.4.SORT. SORT Command
Arguments: sort program Arguments: sort program
charset specification charset specification
searching criteria (one or more) searching criteria (one or more)
Data: untagged responses: SORT Data: untagged responses: SORT
Result: OK - sort completed Result: OK - sort completed
NO - sort error: can't sort that charset or NO - sort error: can't sort that charset or
criteria criteria
BAD - command unknown or arguments invalid BAD - command unknown or arguments invalid
The SORT command is a variant of SEARCH with sorting semantics for The SORT command is a variant of SEARCH with sorting semantics for
the results. Sort has two arguments before the searching criteria the results. Sort has two arguments before the searching criteria
argument; a parenthesized list of sort criteria, and the searching argument; a parenthesized list of sort criteria, and the searching
charset. charset.
The charset argument is mandatory (unlike SEARCH) and indicates The charset argument is mandatory (unlike SEARCH) and indicates
the [CHARSET] of the strings that appear in the searching the [CHARSET] of the strings that appear in the searching
criteria. The US-ASCII and UTF-8 charsets MUST be implemented. criteria. The US-ASCII and UTF-8 charsets MUST be implemented.
All other charsets are optional. All other charsets are optional.
There is also a UID SORT command which returns unique identifiers There is also a UID SORT command which returns unique identifiers
instead of message sequence numbers. Note that there are separate instead of message sequence numbers. Note that there are separate
searching criteria for message sequence numbers and UIDs; thus the searching criteria for message sequence numbers and UIDs; thus the
arguments to UID SORT are interpreted the same as in SORT. This arguments to UID SORT are interpreted the same as in SORT. This
is analogous to the behavior of UID SEARCH, as opposed to UID is analogous to the behavior of UID SEARCH, as opposed to UID
COPY, UID FETCH, or UID STORE. COPY, UID FETCH, or UID STORE.
The SORT command first searches the mailbox for messages that The SORT command first searches the mailbox for messages that
match the given searching criteria using the charset argument for match the given searching criteria using the charset argument for
the interpretation of strings in the searching criteria. It then the interpretation of strings in the searching criteria. It then
returns the matching messages in an untagged SORT response, sorted returns the matching messages in an untagged SORT response, sorted
according to one or more sort criteria. according to one or more sort criteria.
Sorting is in ascending order. Earlier dates sort before later Sorting is in ascending order. Earlier dates sort before later
dates; smaller sizes sort before larger sizes; and strings are dates; smaller sizes sort before larger sizes; and strings are
sorted according to ascending values established by their sorted according to ascending values established by their
collation algorithm (see under "Internationalization collation algorithm (see under "Internationalization
Considerations"). Considerations").
If two or more messages exactly match according to the sorting If two or more messages exactly match according to the sorting
criteria, these messages are sorted according to the order in criteria, these messages are sorted according to the order in
which they appear in the mailbox. In other words, there is an which they appear in the mailbox. In other words, there is an
implicit sort criterion of "sequence number". implicit sort criterion of "sequence number".
When multiple sort criteria are specified, the result is sorted in When multiple sort criteria are specified, the result is sorted in
the priority order that the criteria appear. For example, the priority order that the criteria appear. For example,
(SUBJECT DATE) will sort messages in order by their base subject (SUBJECT DATE) will sort messages in order by their base subject
text; and for messages with the same base subject text will sort text; and for messages with the same base subject text will sort
by their sent date. by their sent date.
Untagged EXPUNGE responses are not permitted while the server is Untagged EXPUNGE responses are not permitted while the server is
responding to a SORT command, but are permitted during a UID SORT responding to a SORT command, but are permitted during a UID SORT
command. command.
The defined sort criteria are as follows. Refer to the Formal The defined sort criteria are as follows. Refer to the Formal
Syntax section for the precise syntactic definitions of the Syntax section for the precise syntactic definitions of the
arguments. If the associated RFC-822 header for a particular arguments. If the associated RFC-822 header for a particular
criterion is absent, it is treated as the empty string. The empty criterion is absent, it is treated as the empty string. The empty
string always collates before non-empty strings. string always collates before non-empty strings.
ARRIVAL ARRIVAL
Internal date and time of the message. This differs from the Internal date and time of the message. This differs from the
ON criteria in SEARCH, which uses just the internal date. ON criteria in SEARCH, which uses just the internal date.
CC CC
[IMAP] addr-mailbox of the first "cc" address. [IMAP] addr-mailbox of the first "cc" address.
DATE DATE
Sent date and time from the Date: header, adjusted by time Sent date and time, as described in section 2.2.
zone. This differs from the SENTON criteria in SEARCH, which
uses just the date and not the time, nor adjusts by time zone.
If the sent date can not be determined (a Date: header is
missing or can not be parsed), the INTERNALDATE for that
message is used as the sent date.
FROM FROM
[IMAP] addr-mailbox of the first "From" address. [IMAP] addr-mailbox of the first "From" address.
REVERSE REVERSE
Followed by another sort criterion, has the effect of that Followed by another sort criterion, has the effect of that
criterion but in reverse (descending) order. criterion but in reverse (descending) order.
Note: REVERSE only reverses a single criterion, and does not Note: REVERSE only reverses a single criterion, and does not
affect the implicit "sequence number" sort criterion if all affect the implicit "sequence number" sort criterion if all
other criteria are identicial. Consequently, a sort of other criteria are identicial. Consequently, a sort of
REVERSE SUBJECT is not the same as a reverse ordering of a REVERSE SUBJECT is not the same as a reverse ordering of a
SUBJECT sort. This can be avoided by use of additional SUBJECT sort. This can be avoided by use of additional
criteria, e.g. SUBJECT DATE vs. REVERSE SUBJECT REVERSE criteria, e.g. SUBJECT DATE vs. REVERSE SUBJECT REVERSE
DATE. In general, however, it's better (and faster, if the DATE. In general, however, it's better (and faster, if the
client has a "reverse current ordering" command) to reverse client has a "reverse current ordering" command) to reverse
the results in the client instead of issuing a new SORT. the results in the client instead of issuing a new SORT.
SIZE SIZE
Size of the message in octets. Size of the message in octets.
SUBJECT SUBJECT
Base subject text. Base subject text.
TO TO
[IMAP] addr-mailbox of the first "To" address. [IMAP] addr-mailbox of the first "To" address.
Example: C: A282 SORT (SUBJECT) UTF-8 SINCE 1-Feb-1994 Example: C: A282 SORT (SUBJECT) UTF-8 SINCE 1-Feb-1994
S: * SORT 2 84 882 S: * SORT 2 84 882
S: A282 OK SORT completed S: A282 OK SORT completed
C: A283 SORT (SUBJECT REVERSE DATE) UTF-8 ALL C: A283 SORT (SUBJECT REVERSE DATE) UTF-8 ALL
S: * SORT 5 3 4 1 2 S: * SORT 5 3 4 1 2
S: A283 OK SORT completed S: A283 OK SORT completed
C: A284 SORT (SUBJECT) US-ASCII TEXT "not in mailbox" C: A284 SORT (SUBJECT) US-ASCII TEXT "not in mailbox"
S: * SORT S: * SORT
S: A284 OK SORT completed S: A284 OK SORT completed
BASE.6.4.THREAD. THREAD Command BASE.6.4.THREAD. THREAD Command
Arguments: threading algorithm Arguments: threading algorithm
charset specification charset specification
searching criteria (one or more) searching criteria (one or more)
Data: untagged responses: THREAD Data: untagged responses: THREAD
Result: OK - thread completed Result: OK - thread completed
NO - thread error: can't thread that charset or NO - thread error: can't thread that charset or
criteria criteria
BAD - command unknown or arguments invalid BAD - command unknown or arguments invalid
The THREAD command is a variant of SEARCH with threading semantics
for the results. Thread has two arguments before the searching
criteria argument; a threading algorithm, and the searching
charset.
The charset argument is mandatory (unlike SEARCH) and indicates The THREAD command is a variant of SEARCH with threading semantics
the [CHARSET] of the strings that appear in the searching for the results. Thread has two arguments before the searching
criteria. The US-ASCII and UTF-8 charsets MUST be implemented. criteria argument; a threading algorithm, and the searching
All other charsets are optional. charset.
There is also a UID THREAD command which returns unique The charset argument is mandatory (unlike SEARCH) and indicates
identifiers instead of message sequence numbers. Note that there the [CHARSET] of the strings that appear in the searching
are separate searching criteria for message sequence numbers and criteria. The US-ASCII and UTF-8 charsets MUST be implemented.
UIDs; thus the arguments to UID THREAD are interpreted the same as All other charsets are optional.
in THREAD. This is analogous to the behavior of UID SEARCH, as
opposed to UID COPY, UID FETCH, or UID STORE.
The THREAD command first searches the mailbox for messages that There is also a UID THREAD command which returns unique
match the given searching criteria using the charset argument for identifiers instead of message sequence numbers. Note that there
the interpretation of strings in the searching criteria. It then are separate searching criteria for message sequence numbers and
returns the matching messages in an untagged THREAD response, UIDs; thus the arguments to UID THREAD are interpreted the same as
threaded according to the specified threading algorithm. in THREAD. This is analogous to the behavior of UID SEARCH, as
opposed to UID COPY, UID FETCH, or UID STORE.
All collation is in ascending order. Earlier dates collate before The THREAD command first searches the mailbox for messages that
later dates and strings are collated according to ascending values match the given searching criteria using the charset argument for
established by their collation algorithm (see under the interpretation of strings in the searching criteria. It then
"Internationalization Considerations"). returns the matching messages in an untagged THREAD response,
threaded according to the specified threading algorithm.
Untagged EXPUNGE responses are not permitted while the server is All collation is in ascending order. Earlier dates collate before
responding to a THREAD command, but are permitted during a UID later dates and strings are collated according to ascending values
THREAD command. established by their collation algorithm (see under
"Internationalization Considerations").
The defined threading algorithms are as follows: Untagged EXPUNGE responses are not permitted while the server is
responding to a THREAD command, but are permitted during a UID
THREAD command.
ORDEREDSUBJECT The defined threading algorithms are as follows:
The ORDEREDSUBJECT threading algorithm is also referred to as ORDEREDSUBJECT
"poor man's threading." The searched messages are sorted by
base subject and then by the sent date. The messages are then
split into separate threads, with each thread containing
messages with the same base subject text. Finally, the threads
are sorted by the sent date of the first message in the thread.
The first message of each thread are siblings of each other The ORDEREDSUBJECT threading algorithm is also referred to as
(the "root"). The second message of a thread is the child of "poor man's threading." The searched messages are sorted by
the first message, and subsequent messages of the thread are base subject and then by the sent date. The messages are then
siblings of the second message and hence children of the split into separate threads, with each thread containing
message at the root. Hence, there are no grandchildren in messages with the same base subject text. Finally, the threads
ORDEREDSUBJECT threading. are sorted by the sent date of the first message in the thread.
Note: early drafts of this specification specified The first message of each thread are siblings of each other
that each message in an ORDEREDSUBJECT thread is a child (the "root"). The second message of a thread is the child of
(as opposed to a sibling) of the previous message. This the first message, and subsequent messages of the thread are
is now deprecated. For compatibility with servers which siblings of the second message and hence children of the
may still use the old definition, client implementations message at the root. Hence, there are no grandchildren in
SHOULD treat descendents of a child as being siblings of ORDEREDSUBJECT threading.
that child.
This is because the old definition mistakenly indicated Children in ORDEREDSUBJECT threading do not have descendents.
that there was a parent/child relationship between Client implementations SHOULD treat descendents of a child in
successive messages in a thread; when in fact there was a server response as being siblings of that child.
only a chronological relationship. In clients which
indicate parent/child relationships in a thread tree,
this would indicate levels of descent which did not
exist.
REFERENCES REFERENCES
The REFERENCES threading algorithm is based on the [THREADING] The REFERENCES threading algorithm threads the searched
algorithm written used in "Netscape Mail and News" versions 2.0 messages by grouping them together in parent/child
through 3.0. This algorithm threads the searched messages by relationships based on which messages are replies to others.
grouping them together in parent/child relationships based on The parent/child relationships are built using two methods:
which messages are replies to others. The parent/child reconstructing a message's ancestry using the references
relationships are built using two methods: reconstructing a contained within it; and checking the original (not base)
message's ancestry using the references contained within it; subject of a message to see if it is a reply to (or forward of)
and checking the original (not base) subject of a message to another message.
see if it is a reply to (or forward of) another message.
Note: "Message ID" in the following description refers to a Note: "Message ID" in the following description refers to a
normalized form of the msg-id in [RFC-2822]. The actual normalized form of the msg-id in [RFC-2822]. The actual
text in an RFC 2822 may use quoting, resulting in multiple text in an RFC 2822 may use quoting, resulting in multiple
ways of expressing the same Message ID. Implementations of ways of expressing the same Message ID. Implementations of
the REFERENCES threading algorithm MUST normalize any msg-id the REFERENCES threading algorithm MUST normalize any msg-id
in order to avoid false non-matches due to differences in in order to avoid false non-matches due to differences in
quoting. quoting.
For example, the msg-id For example, the msg-id
<"01KF8JCEOCBS0045PS"@xxx.yyy.com> <"01KF8JCEOCBS0045PS"@xxx.yyy.com>
and the msg-id and the msg-id
<01KF8JCEOCBS0045PS@xxx.yyy.com> <01KF8JCEOCBS0045PS@xxx.yyy.com>
MUST be interpreted as being the same Message ID. MUST be interpreted as being the same Message ID.
The references used for reconstructing a message's ancestry are The references used for reconstructing a message's ancestry are
found using the following rules: found using the following rules:
If a message contains a References header line, then use the If a message contains a References header line, then use the
Message IDs in the References header line as the references. Message IDs in the References header line as the references.
If a message does not contain a References header line, or If a message does not contain a References header line, or
the References header line does not contain any valid the References header line does not contain any valid
Message IDs, then use the first (if any) valid Message ID Message IDs, then use the first (if any) valid Message ID
found in the In-Reply-To header line as the only reference found in the In-Reply-To header line as the only reference
(parent) for this message. (parent) for this message.
Note: Although [RFC-2822] permits multiple Message IDs in Note: Although [RFC-2822] permits multiple Message IDs in
the In-Reply-To header, in actual practice this the In-Reply-To header, in actual practice this
discipline has not been followed. For example, discipline has not been followed. For example,
In-Reply-To headers have been observed with message In-Reply-To headers have been observed with message
addresses after the Message ID, and there are no good addresses after the Message ID, and there are no good
heuristics for software to determine the difference. heuristics for software to determine the difference.
This is not a problem with the References header however. This is not a problem with the References header however.
If a message does not contain an In-Reply-To header line, or If a message does not contain an In-Reply-To header line, or
the In-Reply-To header line does not contain a valid Message the In-Reply-To header line does not contain a valid Message
ID, then the message does not have any references (NIL). ID, then the message does not have any references (NIL).
A message is considered to be a reply or forward if the base A message is considered to be a reply or forward if the base
subject extraction rules, applied to the original subject, subject extraction rules, applied to the original subject,
remove any of the following: a subj-refwd, a "(fwd)" remove any of the following: a subj-refwd, a "(fwd)"
subj-trailer, or a subj-fwd-hdr and subj-fwd-trl. subj-trailer, or a subj-fwd-hdr and subj-fwd-trl.
The REFERENCES algorithm is significantly more complex than The REFERENCES algorithm is significantly more complex than
ORDEREDSUBJECT and consists of six main steps. These steps are ORDEREDSUBJECT and consists of six main steps. These steps are
outlined in detail below. outlined in detail below.
(1) For each searched message: (1) For each searched message:
(A) Using the Message IDs in the message's references, link (A) Using the Message IDs in the message's references, link
the corresponding messages (those whose Message-ID header the corresponding messages (those whose Message-ID header
line contains the given reference Message ID) together as line contains the given reference Message ID) together as
parent/child. Make the first reference the parent of the parent/child. Make the first reference the parent of the
second (and the second a child of the first), the second the second (and the second a child of the first), the second the
parent of the third (and the third a child of the second), parent of the third (and the third a child of the second),
etc. The following rules govern the creation of these etc. The following rules govern the creation of these
links: links:
If a message does not contain a Message-ID header line, If a message does not contain a Message-ID header line,
or the Message-ID header line does not contain a valid or the Message-ID header line does not contain a valid
Message ID, then assign a unique Message ID to this Message ID, then assign a unique Message ID to this
message. message.
If two or more messages have the same Message ID, then If two or more messages have the same Message ID, then
only use that Message ID in the first (lowest sequence only use that Message ID in the first (lowest sequence
number) message, and assign a unique Message ID to each number) message, and assign a unique Message ID to each
of the subsequent messages with a duplicate of that of the subsequent messages with a duplicate of that
Message ID. Message ID.
If no message can be found with a given Message ID, If no message can be found with a given Message ID,
create a dummy message with this ID. Use this dummy create a dummy message with this ID. Use this dummy
message for all subsequent references to this ID. message for all subsequent references to this ID.
If a message already has a parent, don't change the If a message already has a parent, don't change the
existing link. This is done because the References existing link. This is done because the References
header line may have been truncated by a MUA. As a header line may have been truncated by a MUA. As a
result, there is no guarantee that the messages result, there is no guarantee that the messages
corresponding to adjacent Message IDs in the References corresponding to adjacent Message IDs in the References
header line are parent and child. header line are parent and child.
Do not create a parent/child link if creating that link Do not create a parent/child link if creating that link
would introduce a loop. For example, before making would introduce a loop. For example, before making
message A the parent of B, make sure that A is not a message A the parent of B, make sure that A is not a
descendent of B. descendent of B.
Note: Message ID comparisons are case-sensitive. Note: Message ID comparisons are case-sensitive.
(B) Create a parent/child link between the last reference (B) Create a parent/child link between the last reference
(or NIL if there are no references) and the current message. (or NIL if there are no references) and the current message.
If the current message already has a parent, it is probably If the current message already has a parent, it is probably
the result of a truncated References header line, so break the result of a truncated References header line, so break
the current parent/child link before creating the new the current parent/child link before creating the new
correct one. As in step 1.A, do not create the parent/child correct one. As in step 1.A, do not create the parent/child
link if creating that link would introduce a loop. Note link if creating that link would introduce a loop. Note
that if this message has no references, that it will now that if this message has no references, that it will now
have no parent. have no parent.
Note: The parent/child links created in steps 1.A and 1.B Note: The parent/child links created in steps 1.A and 1.B
MUST be kept consistent with one another at ALL times. MUST be kept consistent with one another at ALL times.
(2) Gather together all of the messages that have no parents (2) Gather together all of the messages that have no parents
and make them all children (siblings of one another) of a dummy and make them all children (siblings of one another) of a dummy
parent (the "root"). These messages constitute the first parent (the "root"). These messages constitute the first
(head) message of the threads created thus far. (head) message of the threads created thus far.
(3) Prune dummy messages from the thread tree. Traverse each (3) Prune dummy messages from the thread tree. Traverse each
thread under the root, and for each message: thread under the root, and for each message:
If it is a dummy message with NO children, delete it. If it is a dummy message with NO children, delete it.
If it is a dummy message with children, delete it, but If it is a dummy message with children, delete it, but
promote its children to the current level. In other words, promote its children to the current level. In other words,
splice them in with the dummy's siblings. splice them in with the dummy's siblings.
Do not promote the children if doing so would make them Do not promote the children if doing so would make them
children of the root, unless there is only one child. children of the root, unless there is only one child.
(4) Sort the messages under the root (top-level siblings only) (4) Sort the messages under the root (top-level siblings only)
by sent date. In the case of an exact match on sent date, use by sent date as described in section 2.2. In the case of a
the order in which the messages appear in the mailbox (that is, dummy message, sort its children by sent date and then use the
by sequence number) to determine the order. In the case of a first child for the top-level sort.
dummy message, sort its children by sent date and then use the
first child for the top-level sort. If the sent date can not
be determined (a Date: header is missing or can not be parsed),
the INTERNALDATE for that message is used as the sent date.
(5) Gather together messages under the root that have the same (5) Gather together messages under the root that have the same
base subject text. base subject text.
(A) Create a table for associating base subjects with (A) Create a table for associating base subjects with
messages, called the subject table. messages, called the subject table.
(B) Populate the subject table with one message per each (B) Populate the subject table with one message per each
base subject. For each child of the root: base subject. For each child of the root:
(i) Find the subject of this thread, by using the base (i) Find the subject of this thread, by using the base
subject from either the current message or its first subject from either the current message or its first
child if the current message is a dummy. This is the child if the current message is a dummy. This is the
thread subject. thread subject.
(ii) If the thread subject is empty, skip this message. (ii) If the thread subject is empty, skip this message.
(iii) Look up the message associated with the thread (iii) Look up the message associated with the thread
subject in the subject table. subject in the subject table.
(iv) If there is no message in the subject table with the (iv) If there is no message in the subject table with the
thread subject, add the current message and the thread thread subject, add the current message and the thread
subject to the subject table. subject to the subject table.
Otherwise, if the message in the subject table is not a Otherwise, if the message in the subject table is not a
dummy, AND either of the following criteria are true: dummy, AND either of the following criteria are true:
The current message is a dummy, OR The current message is a dummy, OR
The message in the subject table is a reply or forward The message in the subject table is a reply or forward
and the current message is not. and the current message is not.
then replace the message in the subject table with the then replace the message in the subject table with the
current message. current message.
(C) Merge threads with the same thread subject. For each (C) Merge threads with the same thread subject. For each
child of the root: child of the root:
(i) Find the message's thread subject as in step 5.B.i (i) Find the message's thread subject as in step 5.B.i
above. above.
(ii) If the thread subject is empty, skip this message. (ii) If the thread subject is empty, skip this message.
(iii) Lookup the message associated with this thread (iii) Lookup the message associated with this thread
subject in the subject table. subject in the subject table.
(iv) If the message in the subject table is the current (iv) If the message in the subject table is the current
message, skip this message. message, skip this message.
Otherwise, merge the current message with the one in the Otherwise, merge the current message with the one in the
subject table using the following rules: subject table using the following rules:
If both messages are dummies, append the current If both messages are dummies, append the current
message's children to the children of the message in message's children to the children of the message in
the subject table (the children of both messages the subject table (the children of both messages
become siblings), and then delete the current message. become siblings), and then delete the current message.
If the message in the subject table is a dummy and the If the message in the subject table is a dummy and the
current message is not, make the current message a current message is not, make the current message a
child of the message in the subject table (a sibling child of the message in the subject table (a sibling
of its children). of its children).
If the current message is a reply or forward and the If the current message is a reply or forward and the
message in the subject table is not, make the current message in the subject table is not, make the current
message a child of the message in the subject table (a message a child of the message in the subject table (a
sibling of its children). sibling of its children).
Otherwise, create a new dummy message and make both Otherwise, create a new dummy message and make both
the current message and the message in the subject the current message and the message in the subject
table children of the dummy. Then replace the message table children of the dummy. Then replace the message
in the subject table with the dummy message. in the subject table with the dummy message.
Note: Subject comparisons are case-insensitive, as Note: Subject comparisons are case-insensitive, as
described under "Internationalization described under "Internationalization
Considerations." Considerations."
(6) Traverse the messages under the root and sort each set of (6) Traverse the messages under the root and sort each set of
siblings by sent date. Traverse the messages in such a way siblings by sent date as described in section 2.2. Traverse
that the "youngest" set of siblings are sorted first, and the the messages in such a way that the "youngest" set of siblings
"oldest" set of siblings are sorted last (grandchildren are are sorted first, and the "oldest" set of siblings are sorted
sorted before children, etc). In the case of an exact match on last (grandchildren are sorted before children, etc). In the
sent date or if either of the Date: headers used in a case of a dummy message (which can only occur with top-level
comparison can not be parsed, use the order in which the siblings), use its first child for sorting.
messages appear in the mailbox (that is, by sequence number) to
determine the order. In the case of a dummy message (which can
only occur with top-level siblings), use its first child for
sorting.
Example: C: A283 THREAD ORDEREDSUBJECT UTF-8 SINCE 5-MAR-2000 Example: C: A283 THREAD ORDEREDSUBJECT UTF-8 SINCE 5-MAR-2000
S: * THREAD (166)(167)(168)(169)(172)(170)(171) S: * THREAD (166)(167)(168)(169)(172)(170)(171)
(173)(174 (175)(176)(178)(181)(180))(179)(177 (173)(174 (175)(176)(178)(181)(180))(179)(177
(183)(182)(188)(184)(185)(186)(187)(189))(190) (183)(182)(188)(184)(185)(186)(187)(189))(190)
(191)(192)(193)(194 195)(196 (197)(198))(199) (191)(192)(193)(194 195)(196 (197)(198))(199)
(200 202)(201)(203)(204)(205)(206 207)(208) (200 202)(201)(203)(204)(205)(206 207)(208)
S: A283 OK THREAD completed S: A283 OK THREAD completed
C: A284 THREAD ORDEREDSUBJECT US-ASCII TEXT "gewp" C: A284 THREAD ORDEREDSUBJECT US-ASCII TEXT "gewp"
S: * THREAD S: * THREAD
S: A284 OK THREAD completed S: A284 OK THREAD completed
C: A285 THREAD REFERENCES UTF-8 SINCE 5-MAR-2000 C: A285 THREAD REFERENCES UTF-8 SINCE 5-MAR-2000
S: * THREAD (166)(167)(168)(169)(172)((170)(179)) S: * THREAD (166)(167)(168)(169)(172)((170)(179))
(171)(173)((174)(175)(176)(178)(181)(180)) (171)(173)((174)(175)(176)(178)(181)(180))
((177)(183)(182)(188 (184)(189))(185 186)(187)) ((177)(183)(182)(188 (184)(189))(185 186)(187))
(190)(191)(192)(193)((194)(195 196))(197 198) (190)(191)(192)(193)((194)(195 196))(197 198)
(199)(200 202)(201)(203)(204)(205 206 207)(208) (199)(200 202)(201)(203)(204)(205 206 207)(208)
S: A285 OK THREAD completed S: A285 OK THREAD completed
Note: The line breaks in the first and third server Note: The line breaks in the first and third server
responses are for editorial clarity and do not appear in responses are for editorial clarity and do not appear in
real THREAD responses. real THREAD responses.
4. Additional Responses 4. Additional Responses
These responses are extensions to the [IMAP] base protocol. These responses are extensions to the [IMAP] base protocol.
The section headings of these responses are intended to correspond The section headings of these responses are intended to correspond
with where they would be located in the main document. with where they would be located in the main document.
BASE.7.2.SORT. SORT Response BASE.7.2.SORT. SORT Response
Data: zero or more numbers Data: zero or more numbers
The SORT response occurs as a result of a SORT or UID SORT The SORT response occurs as a result of a SORT or UID SORT
command. The number(s) refer to those messages that match the command. The number(s) refer to those messages that match the
search criteria. For SORT, these are message sequence numbers; search criteria. For SORT, these are message sequence numbers;
for UID SORT, these are unique identifiers. Each number is for UID SORT, these are unique identifiers. Each number is
delimited by a space. delimited by a space.
Example: S: * SORT 2 3 6 Example: S: * SORT 2 3 6
BASE.7.2.THREAD. THREAD Response BASE.7.2.THREAD. THREAD Response
Data: zero or more threads Data: zero or more threads
The THREAD response occurs as a result of a THREAD or UID THREAD The THREAD response occurs as a result of a THREAD or UID THREAD
command. It contains zero or more threads. A thread consists of command. It contains zero or more threads. A thread consists of
a parenthesized list of thread members. a parenthesized list of thread members.
Thread members consist of zero or more message numbers, delimited Thread members consist of zero or more message numbers, delimited
by spaces, indicating successive parent and child. This continues by spaces, indicating successive parent and child. This continues
until the thread splits into multiple sub-threads, at which point until the thread splits into multiple sub-threads, at which point
the thread nests into multiple sub-threads with the first member the thread nests into multiple sub-threads with the first member
of each subthread being siblings at this level. There is no limit of each subthread being siblings at this level. There is no limit
to the nesting of threads. to the nesting of threads.
The messages numbers refer to those messages that match the search The messages numbers refer to those messages that match the search
criteria. For THREAD, these are message sequence numbers; for UID criteria. For THREAD, these are message sequence numbers; for UID
THREAD, these are unique identifiers. THREAD, these are unique identifiers.
Example: S: * THREAD (2)(3 6 (4 23)(44 7 96)) Example: S: * THREAD (2)(3 6 (4 23)(44 7 96))
The first thread consists only of message 2. The second thread The first thread consists only of message 2. The second thread
consists of the messages 3 (parent) and 6 (child), after which it consists of the messages 3 (parent) and 6 (child), after which it
splits into two subthreads; the first of which contains messages 4 splits into two subthreads; the first of which contains messages 4
(child of 6, sibling of 44) and 23 (child of 4), and the second of (child of 6, sibling of 44) and 23 (child of 4), and the second of
which contains messages 44 (child of 6, sibling of 4), 7 (child of which contains messages 44 (child of 6, sibling of 4), 7 (child of
44), and 96 (child of 7). Since some later messages are parents 44), and 96 (child of 7). Since some later messages are parents
of earlier messages, the messages were probably moved from some of earlier messages, the messages were probably moved from some
other mailbox at different times. other mailbox at different times.
-- 2 -- 2
-- 3 -- 3
\-- 6 \-- 6
|-- 4 |-- 4
| \-- 23 | \-- 23
| |
\-- 44 \-- 44
\-- 7 \-- 7
\-- 96 \-- 96
Example: S: * THREAD ((3)(5)) Example: S: * THREAD ((3)(5))
In this example, 3 and 5 are siblings of a parent which does not In this example, 3 and 5 are siblings of a parent which does not
match the search criteria (and/or does not exist in the mailbox); match the search criteria (and/or does not exist in the mailbox);
however they are members of the same thread. however they are members of the same thread.
5. Formal Syntax of SORT and THREAD Commands and Responses 5. Formal Syntax of SORT and THREAD Commands and Responses
The following syntax specification uses the Augmented Backus-Naur The following syntax specification uses the Augmented Backus-Naur
Form (ABNF) notation as specified in [ABNF]. It also uses [ABNF] Form (ABNF) notation as specified in [ABNF]. It also uses [ABNF]
rules defined in [IMAP]. rules defined in [IMAP].
sort = ["UID" SP] "SORT" SP sort-criteria SP search-criteria sort = ["UID" SP] "SORT" SP sort-criteria SP search-criteria
sort-criteria = "(" sort-criterion *(SP sort-criterion) ")" sort-criteria = "(" sort-criterion *(SP sort-criterion) ")"
sort-criterion = ["REVERSE" SP] sort-key sort-criterion = ["REVERSE" SP] sort-key
sort-key = "ARRIVAL" / "CC" / "DATE" / "FROM" / "SIZE" / sort-key = "ARRIVAL" / "CC" / "DATE" / "FROM" / "SIZE" /
"SUBJECT" / "TO" "SUBJECT" / "TO"
thread = ["UID" SP] "THREAD" SP thread-alg SP search-criteria thread = ["UID" SP] "THREAD" SP thread-alg SP search-criteria
thread-alg = "ORDEREDSUBJECT" / "REFERENCES" / thread-alg-ext thread-alg = "ORDEREDSUBJECT" / "REFERENCES" / thread-alg-ext
thread-alg-ext = atom thread-alg-ext = atom
; New algorithms MUST be registered with IANA ; New algorithms MUST be registered with IANA
search-criteria = charset 1*(SP search-key) search-criteria = charset 1*(SP search-key)
charset = atom / quoted charset = atom / quoted
; CHARSET values MUST be registered with IANA ; CHARSET values MUST be registered with IANA
sort-data = "SORT" *(SP nz-number) sort-data = "SORT" *(SP nz-number)
thread-data = "THREAD" [SP 1*thread-list] thread-data = "THREAD" [SP 1*thread-list]
thread-list = "(" (thread-members / thread-nested) ")" thread-list = "(" (thread-members / thread-nested) ")"
thread-members = nz-number *(SP nz-number) [SP thread-nested] thread-members = nz-number *(SP nz-number) [SP thread-nested]
thread-nested = 2*thread-list thread-nested = 2*thread-list
The following syntax describes base subject extraction rules (2)-(6): The following syntax describes base subject extraction rules (2)-(6):
subject = *subj-leader [subj-middle] *subj-trailer subject = *subj-leader [subj-middle] *subj-trailer
subj-refwd = ("re" / ("fw" ["d"])) *WSP [subj-blob] ":" subj-refwd = ("re" / ("fw" ["d"])) *WSP [subj-blob] ":"
subj-blob = "[" *BLOBCHAR "]" *WSP subj-blob = "[" *BLOBCHAR "]" *WSP
subj-fwd = subj-fwd-hdr subject subj-fwd-trl subj-fwd = subj-fwd-hdr subject subj-fwd-trl
subj-fwd-hdr = "[fwd:" subj-fwd-hdr = "[fwd:"
subj-fwd-trl = "]" subj-fwd-trl = "]"
subj-leader = (*subj-blob subj-refwd) / WSP subj-leader = (*subj-blob subj-refwd) / WSP
subj-middle = *subj-blob (subj-base / subj-fwd) subj-middle = *subj-blob (subj-base / subj-fwd)
; last subj-blob is subj-base if subj-base would ; last subj-blob is subj-base if subj-base would
; otherwise be empty ; otherwise be empty
subj-trailer = "(fwd)" / WSP subj-trailer = "(fwd)" / WSP
subj-base = NONWSP *(*WSP NONWSP) subj-base = NONWSP *(*WSP NONWSP)
; can be a subj-blob ; can be a subj-blob
BLOBCHAR = %x01-5a / %x5c / %x5e-ff BLOBCHAR = %x01-5a / %x5c / %x5e-ff
; any CHAR8 except '[' and ']' ; any CHAR8 except '[' and ']'
NONWSP = %x01-08 / %x0a-1f / %x21-ff NONWSP = %x01-08 / %x0a-1f / %x21-ff
; any CHAR8 other than WSP ; any CHAR8 other than WSP
6. Security Considerations 6. Security Considerations
The SORT and THREAD extensions do not raise any security The SORT and THREAD extensions do not raise any security
considerations that are not present in the base [IMAP] protocol, and considerations that are not present in the base [IMAP] protocol, and
these issues are discussed in [IMAP]. Nevertheless, it is important these issues are discussed in [IMAP]. Nevertheless, it is important
to remember that [IMAP] protocol transactions, including message to remember that [IMAP] protocol transactions, including message
data, are sent in the clear over the network unless protection from data, are sent in the clear over the network unless protection from
snooping is negotiated, either by the use of STARTTLS, privacy snooping is negotiated, either by the use of STARTTLS, privacy
protection is negotiated in the AUTHENTICATE command, or some other protection is negotiated in the AUTHENTICATE command, or some other
protection mechanism is in effect. protection mechanism.
7. Internationalization Considerations Although not a security consideration, it is important to recognize
that sorting by REFERENCES can lead to misleading threading trees.
For example, a message with false References: header data will cause
a thread to be incorporated into another thread.
As stated in the introduction, the server SHOULD support the The process of extracting the base subject may lead to incorrect
[IMAP-I18N] COMPARATOR extension and follow its rules to perform collation if the extracted data was significant text as opposed to
collations in the SORT and THREAD extensions. a subject artifact.
If the server does not support COMPARATOR, strings MUST be collated 7. Internationalization Considerations
according to the i;unicode-casemap collation described in
[UNICASEMAP].
As described in [IMAP-I18N], strings in charsets other than US-ASCII As stated in the introduction, the rules of I18NLEVEL=1 as described
and UTF-8 MUST be converted to UTF-8 and compared in ascending order in [IMAP-I18N] MUST be followed; that is, the SORT and THREAD
according to the selected or active collation algorithm. If the extensions MUST collate strings according to the i;unicode-casemap
server does not support the [IMAP-I18N] COMPARATOR extension, the collation described in [UNICASEMAP]. Servers SHOULD also advertise
collation algorithm used is the "en;ascii-casemap" collation the I18NLEVEL=1 extension. Alternatively, a server MAY implement
described in [COMPARATOR]. I18NLEVEL=2 (or higher) and comply with the rules of that level.
Translations of the "re" or "fw"/"fwd" tokens are not specified for As discussed in [IMAP-I18N] section 4.5, all server implementations
removal in the base subject extraction process. An attempt to add should eventually be updated to support the [IMAP-I18N] I18NLEVEL=2
such translated tokens would result in a geometrically complex, and extension.
ultimately unimplementable, task.
Instead, note that [RFC-2822] section 3.6.5 recommends that "re:" Translations of the "re" or "fw"/"fwd" tokens are not specified for
(from the Latin "res", in the matter of) be used to identify a reply. removal in the base subject extraction process. An attempt to add
Although it is evident that, from the multiple forms of token to such translated tokens would result in a geometrically complex, and
identify a forwarded message, there is considerable variation found ultimately unimplementable, task.
in the wild, the variations are (still) manageable. Consequently, it
is suggested that "re:" and one of the variations of the tokens for Instead, note that [RFC-2822] section 3.6.5 recommends that "re:"
forward supported by the base subject extraction rules be adopted for (from the Latin "res", in the matter of) be used to identify a reply.
Internet mail messages, since doing so makes it a simple display time Although it is evident that, from the multiple forms of token to
task to localize the token language for the user. identify a forwarded message, there is considerable variation found
in the wild, the variations are (still) manageable. Consequently, it
is suggested that "re:" and one of the variations of the tokens for
forward supported by the base subject extraction rules be adopted for
Internet mail messages, since doing so makes it a simple display time
task to localize the token language for the user.
8. IANA Considerations 8. IANA Considerations
[IMAP] capabilities are registered by publishing a standards track or [IMAP] capabilities are registered by publishing a standards track or
IESG approved experimental RFC. This document constitutes IESG approved experimental RFC. This document constitutes
registration of the SORT and THREAD capabilities in the [IMAP] registration of the SORT and THREAD capabilities in the [IMAP]
capabilities registry. capabilities registry.
This document creates a new [IMAP] threading algorithms registry, This document creates a new [IMAP] threading algorithms registry,
which registers threading algorithms by publishing a standards track which registers threading algorithms by publishing a standards track
or IESG approved experimental RFC. This document constitutes or IESG approved experimental RFC. This document constitutes
registration of the ORDEREDSUBJECT and REFERENCES algorithms in that registration of the ORDEREDSUBJECT and REFERENCES algorithms in that
registry. registry.
9. Normative References 9. Normative References
The following documents are normative to this document: The following documents are normative to this document:
[ABNF] Crocker, D. and Overell, P. "Augmented BNF
for Syntax Specifications: ABNF", RFC 4234
October 2005.
[CHARSET] Freed, N. and Postel, J. "IANA Character Set [ABNF] Crocker, D. and Overell, P. "Augmented BNF
Registration Procedures", RFC 2978, October for Syntax Specifications: ABNF", RFC 5234
2000. January 2008
[COMPARATOR] Newman, C. and Duerst, M. "Internet [CHARSET] Freed, N. and Postel, J. "IANA Character Set
Appplication Protocol Collation Registry", Registration Procedures", RFC 2978, October
RFC 4790, March 2007 2000.
[IMAP] Crispin, M. "Internet Message Access Protocol - [IMAP] Crispin, M. "Internet Message Access Protocol -
Version 4rev1", RFC 3501, March 2003. Version 4rev1", RFC 3501, March 2003.
[IMAP-I18N] Newman, C. and Gulbrandsen, A. "Internet [IMAP-I18N] Newman, C. and Gulbrandsen, A. "Internet
Message Access Protocol Internationalization", Message Access Protocol Internationalization",
Work in Progress. Work in Progress.
[KEYWORDS] Bradner, S. "Key words for use in RFCs to [KEYWORDS] Bradner, S. "Key words for use in RFCs to
Indicate Requirement Levels", BCP 14, RFC 2119, Indicate Requirement Levels", BCP 14, RFC 2119,
March 1997. March 1997.
[RFC-2822] Resnick, P. "Internet Message Format", RFC [RFC-2822] Resnick, P. "Internet Message Format", RFC
2822, April 2001. 2822, April 2001.
[UNICASEMAP] Crispin, M. "i;unicode-casemap - Simple Unicode [UNICASEMAP] Crispin, M. "i;unicode-casemap - Simple Unicode
Collation Algorithm", Work in Progress. Collation Algorithm", RFC 5051.
10. Informative References 10. Informative References
The following documents are informative to this document: The following documents are informative to this document:
[IMAP-MODELS] Crispin, M. "Distributed Electronic Mail Models [IMAP-MODELS] Crispin, M. "Distributed Electronic Mail Models
in IMAP4", RFC 1733, December 1994. in IMAP4", RFC 1733, December 1994.
[THREADING] Zawinski, J. "Message Threading", [THREADING] Zawinski, J. "Message Threading",
http://www.jwz.org/doc/threading.html, http://www.jwz.org/doc/threading.html,
1997-2002. 1997-2002.
Appendices Appendices
Author's Address Author's Address
Mark R. Crispin Mark R. Crispin
Networks and Distributed Computing Networks and Distributed Computing
University of Washington University of Washington
4545 15th Avenue NE 4545 15th Avenue NE
Seattle, WA 98105-4527 Seattle, WA 98105-4527
Phone: +1 (206) 543-5762 Phone: +1 (206) 543-5762
EMail: MRC@CAC.Washington.EDU EMail: MRC@CAC.Washington.EDU
Kenneth Murchison Kenneth Murchison
Carnegie Mellon University Carnegie Mellon University
5000 Forbes Avenue 5000 Forbes Avenue
Cyert Hall 285 Cyert Hall 285
Pittsburgh, PA 15213 Pittsburgh, PA 15213
Phone: +1 (412) 268-2638 Phone: +1 (412) 268-2638
Email: murch@andrew.cmu.edu Email: murch@andrew.cmu.edu
Full Copyright Statement Full Copyright Statement
Copyright (C) The IETF Trust (2007). Copyright (C) The IETF Trust (2008).
This document is subject to the rights, licenses and restrictions This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors contained in BCP 78, and except as set forth therein, the authors
retain all their rights. retain all their rights.
This document and the information contained herein are provided on an This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Intellectual Property Intellectual Property
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Acknowledgement Acknowledgement
Funding for the RFC Editor function is currently provided by the Funding for the RFC Editor function is currently provided by the
Internet Society. Internet Society.
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