draft-ietf-imapext-sort-17.txt   draft-ietf-imapext-sort-18.txt 
IMAP Extensions Working Group M. Crispin IMAP Extensions Working Group M. Crispin
INTERNET-DRAFT: IMAP SORT K. Murchison INTERNET-DRAFT: IMAP SORT K. Murchison
Document: internet-drafts/draft-ietf-imapext-sort-18.txt November 2006
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. A server which with "SORT", indicating support for this base level.
implements the SORT extension SHOULD also implement the COMPARATOR
extension as described in [IMAP-I18N].
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
also implement the COMPARATOR extension as described in [IMAP-I18N].
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", "MAY", and "OPTIONAL" in this document are to "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
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
actual "base subject" which is used to sort by subject, using the "base subject", using the [ABNF] formal syntax rules described in
[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.
skipping to change at line 115 skipping to change at line 121
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-MODEL]) clients All servers and disconnected (as described in [IMAP-MODELS]) clients
MUST use exactly this algorithm when sorting by subject. Otherwise MUST use exactly this algorithm to determine the "base subject".
there is potential for a user to get inconsistent results based on Otherwise there is potential for a user to get inconsistent results
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 UTC. time from the Date: header, adjusted by time zone to normalize to
For example, "31 Dec 2000 16:01:33 -0800" is equivalent to the UTC UTC. For example, "31 Dec 2000 16:01:33 -0800" is equivalent to the
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 UTC. If the time zone is invalid, the date and time SHOULD be treated as
If the time is also invalid, the time SHOULD be treated as 00:00:00. If UTC. If the time is also invalid, the time SHOULD be treated as
there is no valid date or time, the date and time SHOULD be treated as 00:00:00. If there is no valid date or time, the date and time
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.
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
skipping to change at line 163 skipping to change at line 169
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 criteria. the [CHARSET] of the strings that appear in the searching
The US-ASCII and UTF-8 charsets MUST be implemented. All other criteria. The US-ASCII and UTF-8 charsets MUST be implemented.
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 is arguments to UID SORT are interpreted the same as in SORT. This
analogous to the behavior of UID SEARCH, as opposed to UID COPY, UID is analogous to the behavior of UID SEARCH, as opposed to 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
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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
RFC-822 local-part 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 from the Date: header, adjusted by time
zone. This differs from the SENTON criteria in SEARCH, which zone. This differs from the SENTON criteria in SEARCH, which
uses just the date and not the time, nor adjusts by time zone. uses just the date and not the time, nor adjusts by time zone.
FROM FROM
RFC-822 local-part 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
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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
RFC-822 local-part 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
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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 The THREAD command is a variant of SEARCH with threading semantics
for the results. Thread has two arguments before the searching for the results. Thread has two arguments before the searching
criteria argument; a threading algorithm, and the searching criteria argument; a threading algorithm, 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 criteria. the [CHARSET] of the strings that appear in the searching
The US-ASCII and UTF-8 charsets MUST be implemented. All other criteria. The US-ASCII and UTF-8 charsets MUST be implemented.
charsets are optional. All other charsets are optional.
There is also a UID THREAD command which returns unique identifiers There is also a UID THREAD command which returns unique
instead of message sequence numbers. Note that there are separate identifiers instead of message sequence numbers. Note that there
searching criteria for message sequence numbers and UIDs; thus the are separate searching criteria for message sequence numbers and
arguments to UID THREAD are interpreted the same as in THREAD. This is UIDs; thus the arguments to UID THREAD are interpreted the same as
analogous to the behavior of UID SEARCH, as opposed to UID COPY, UID in THREAD. This is analogous to the behavior of UID SEARCH, as
FETCH, or UID STORE. opposed to UID COPY, UID FETCH, or UID STORE.
The THREAD command first searches the mailbox for messages that The THREAD 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 THREAD response, returns the matching messages in an untagged THREAD response,
threaded according to the specified threading algorithm. threaded according to the specified threading algorithm.
All collation is in ascending order. Earlier dates collate before All collation is in ascending order. Earlier dates collate before
later dates and strings are collated according to ascending values later dates and strings are collated according to ascending values
established by their collation algorithm (see under established by their collation algorithm (see under
"Internationalization Considerations"). "Internationalization Considerations").
Untagged EXPUNGE responses are not permitted while the server is
responding to a THREAD command, but are permitted during a UID
THREAD command.
The defined threading algorithms are as follows: The defined threading algorithms are as follows:
ORDEREDSUBJECT ORDEREDSUBJECT
The ORDEREDSUBJECT threading algorithm is also referred to as The ORDEREDSUBJECT threading algorithm is also referred to as
"poor man's threading." The searched messages are sorted by "poor man's threading." The searched messages are sorted by
base subject and then by the sent date. The messages are then base subject and then by the sent date. The messages are then
split into separate threads, with each thread containing split into separate threads, with each thread containing
messages with the same base subject text. Finally, the threads messages with the same base subject text. Finally, the threads
are sorted by the sent date of the first message in the thread. are sorted by the sent date of the first message in the thread.
skipping to change at line 342 skipping to change at line 352
algorithm written used in "Netscape Mail and News" versions 2.0 algorithm written used in "Netscape Mail and News" versions 2.0
through 3.0. This algorithm threads the searched messages by through 3.0. This algorithm threads the searched messages by
grouping them together in parent/child relationships based on grouping them together in parent/child relationships based on
which messages are replies to others. The parent/child which messages are replies to others. The parent/child
relationships are built using two methods: reconstructing a relationships are built using two methods: reconstructing a
message's ancestry using the references contained within it; message's ancestry using the references contained within it;
and checking the original (not base) subject of a message to and checking the original (not base) subject of a message to
see if it is a reply to (or forward of) 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>
skipping to change at line 367 skipping to change at line 377
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).
skipping to change at line 459 skipping to change at line 469
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 or if by sent date. In the case of an exact match on sent date, use
either of the Date: headers used in a comparison can not be the order in which the messages appear in the mailbox (that is,
parsed, use the order in which the messages appear in the by sequence number) to determine the order. In the case of a
mailbox (that is, by sequence number) to determine the order. dummy message, sort its children by sent date and then use the
In the case of a dummy message, sort its children by sent date first child for the top-level sort. If the sent date can not
and then use the first child for the top-level sort. 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:
skipping to change at line 571 skipping to change at line 582
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 client 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.
skipping to change at line 665 skipping to change at line 676
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 = astring 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]
skipping to change at line 703 skipping to change at line 714
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-7f BLOBCHAR = %x01-5a / %x5c / %x5e-ff
; any CHAR except '[' and ']' ; any CHAR8 except '[' and ']'
NONWSP = %x01-08 / %x0a-1f / %x21-7f NONWSP = %x01-08 / %x0a-1f / %x21-ff
; any CHAR 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 is in effect.
7. Internationalization Considerations 7. Internationalization Considerations
As described in [IMAP-I18N], strings in charsets other than US-ASCII As described in [IMAP-I18N], strings in charsets other than US-ASCII
and UTF-8 MUST be converted to UTF-8 and compared in ascending order and UTF-8 MUST be converted to UTF-8 and compared in ascending order
according to the selected or active collation algorithm. If the server according to the selected or active collation algorithm. If the
does not support the [IMAP-I18N] COMPARATOR extension, the collation server does not support the [IMAP-I18N] COMPARATOR extension, the
algorithm used is the "en;ascii-casemap" collation described in collation algorithm used is the "en;ascii-casemap" collation
[COMPARATOR]. described in [COMPARATOR].
Translations of the "re" or "fw"/"fwd" tokens are not specified for Translations of the "re" or "fw"/"fwd" tokens are not specified for
removal in the base subject extraction process. An attempt to add such removal in the base subject extraction process. An attempt to add
translated tokens would result in a geometrically complex, and such translated tokens would result in a geometrically complex, and
ultimately unimplementable, task. ultimately unimplementable, task.
Instead, note that [RFC-2822] section 3.6.5 recommends that "re:" (from Instead, note that [RFC-2822] section 3.6.5 recommends that "re:"
the Latin "res", in the matter of) be used to identify a reply. (from the Latin "res", in the matter of) be used to identify a reply.
Although it is evident that, from the multiple forms of token to Although it is evident that, from the multiple forms of token to
identify a forwarded message, there is considerable variation found in identify a forwarded message, there is considerable variation found
the wild, the variations are (still) manageable. Consequently, it is in the wild, the variations are (still) manageable. Consequently, it
suggested that "re:" and one of the variations of the tokens for forward is suggested that "re:" and one of the variations of the tokens for
supported by the base subject extraction rules be adopted for Internet forward supported by the base subject extraction rules be adopted for
mail messages, since doing so makes it a simple display time task to Internet mail messages, since doing so makes it a simple display time
localize the token language for the user. 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 registration IESG approved experimental RFC. This document constitutes
of the SORT and THREAD capabilities in the [IMAP] capabilities registry. registration of the SORT and THREAD capabilities in the [IMAP]
capabilities registry.
This document creates a new [IMAP] threading algorithms registry, which
registers threading algorithms by publishing a standards track or IESG
approved experimental RFC. This document constitutes registration of
the ORDEREDSUBJECT and REFERENCES algorithms in that registry.
Appendices This document creates a new [IMAP] threading algorithms registry,
which registers threading algorithms by publishing a standards track
or IESG approved experimental RFC. This document constitutes
registration of the ORDEREDSUBJECT and REFERENCES algorithms in that
registry.
A. 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 [ABNF] Crocker, D. and Overell, P. "Augmented BNF
for Syntax Specifications: ABNF", RFC 2234, for Syntax Specifications: ABNF", RFC 4234
November 1997. October 2005.
[CHARSET] Freed, N. and J. Postel, "IANA Character Set [CHARSET] Freed, N. and J. Postel, "IANA Character Set
Registration Procedures", RFC 2978, October Registration Procedures", RFC 2978, October
2000. 2000.
[COMPARATOR] Newman, C. "Internet Appplication Protocol [COMPARATOR] Newman, C. "Internet Appplication Protocol
Collation Registry", Work in Progress. Collation Registry", Work in Progress.
[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. "Internet Message Access Protocol [IMAP-I18N] Newman, C. "Internet Message Access Protocol
Internationalization", Work in Progress. Internationalization", 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", RFC 2119, Harvard Indicate Requirement Levels", BCP 14, RFC 2119,
University, March 1997. March 1997.
[RFC-2822] Resnick, P. "Internet Message Format", RFC 2822, [RFC-2822] Resnick, P. "Internet Message Format", RFC
April 2001. 2822, April 2001.
B. 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, 1997-2002. http://www.jwz.org/doc/threading.html,
1997-2002.
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: (206) 543-5762 Phone: +1 (206) 543-5762
EMail: MRC@CAC.Washington.EDU EMail: MRC@CAC.Washington.EDU
Kenneth Murchison Kenneth Murchison
Oceana Matrix Ltd. Carnegie Mellon University
21 Princeton Place 5000 Forbes Avenue
Orchard Park, NY 14127 Cyert Hall 285
Pittsburgh, PA 15213
Phone: (716) 662-8973 x26
EMail: ken@oceana.com
IPR Disclosure Acknowledgement
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and any of which I become aware will be disclosed, in accordance with
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The IETF invites any interested party to bring to its attention any Phone: +1 (412) 268-2638
copyrights, patents or patent applications, or other proprietary Email: murch@andrew.cmu.edu
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Full Copyright Statement Full Copyright Statement
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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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