Pete Maclean | 20 Mar 17:10 2015

Re: The IMAP APPENDLIMIT Extension - version 04

Thanks, Bron.  I am aware of Java's lack of unsigned integers having 
had to work around it before.  (I find it a curious lack although I 
have no idea of the rationale behind it.)  So, yes, I come to agree 
that UINT64_MAX would be a poor choice, never mind an unnecessarily 
large one.  So how about a compromise of, say, UINT48_MAX?

Pete

At 02:18 AM 3/19/2015, Bron Gondwana wrote:
>On Thu, Mar 19, 2015, at 09:02 AM, Pete Maclean wrote:
> >
> > >1.  APPENDLIMIT value should be UINT32_MAX or UINT64_MAX ?
> >
> > UINT64_MAX
>
>Most of the world is going with half that in new standards, for
>compatibility with languages that offer a signed 64 bit numeric value
>only (aka - java 7 and below).  It makes mapping the values through said
>languages a lot easier, and 63 bits should be enough for anyone (or
>something).
>
>Alternatively, there's 53 bits, which is the maximum that javascript can
>represent:
>
>http://stackoverflow.com/questions/307179/what-is-javascripts-highest-integer-value-that-a-number-can-go-to-without-losin
>
>It's not going to matter in practice, because that's still fricking huge.
>
>Bron.
>
(Continue reading)

Pete Maclean | 18 Mar 23:02 2015

Re: The IMAP APPENDLIMIT Extension - version 04


>1.  APPENDLIMIT value should be UINT32_MAX or UINT64_MAX ?

UINT64_MAX

>2.  APPENDLIMIT value in SELECT/STATUS response: Whether APPENDLIMIT 
>is needed in both SELECT

I don't feel strongly about this but, considering the recent 
arguments on the matter, I lean toward having it only in STATUS.

Pete Maclean

>and STATUS response?
At 03:47 PM 3/18/2015, Jayantheesh S B wrote:
>All,
>
>Can you please share your views regarding the below item to come to 
>a consensus?
>
>1.  APPENDLIMIT value should be UINT32_MAX or UINT64_MAX ?
>
>2.  APPENDLIMIT value in SELECT/STATUS response: Whether APPENDLIMIT 
>is needed in both SELECT and STATUS response?
>
>Please share your thoughts.
>
>Regards,
>Jay
>
(Continue reading)

Valerio Valerio | 12 Mar 08:06 2015

NIL boundary in multipart emails

Hi All,

while chasing a bug in our IMAP implementation noticed that one server 
replies to a BODYSTRUCTURE fetch command with a structure containing NIL 
boundary for multipart emails, e.g:

SEND UID FETCH 36 (FLAGS UID INTERNALDATE RFC822.SIZE BODYSTRUCTURE 
RFC822.HEADER)
RECV: * 7 FETCH (FLAGS (\Unseen) UID 36 INTERNALDATE "12-Mar-2015 
09:25:30 +0300" RFC822.SIZE 18142 BODYSTRUCTURE (("text" "plain" 
("charset" "utf-8") NIL NIL "quoted-printable" 34433 0 NIL NIL NIL 
NIL)("text" "html" ("charset" "utf-8") NIL NIL "quoted-printable" 108403 
0 NIL NIL NIL NIL) "alternative" ("boundary" NIL)) RFC822.HEADER {2558}

I can gracefully handle this situation, but by my understanding of RFC 
2046[1], this is invalid, first the boundary does exist and is not empty 
and in case it was empty server should send something like "". Since 
this server always reply like that and is a big provider in 
Russia(mail.ru) I was wondering if I'm missing something here ?

Thanks in advance.

Best regards,

Valério

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(Continue reading)

Jayantheesh S B | 10 Mar 22:08 2015

IMAP COMPRESS=DEFLATE Support

All,

 

I am facing an issue with IMAP COMPRESS=DEFLATE feature. After COMPRESS DEFLATE command,

deflate stream is opened and sent the NAMESPACE request to server.  Request is sent successfully, but response was not received.

 

After Socket read timeout, it’s coming out from the Read block. Currently I am using java.util.zip.* package for creating the deflate stream.

Please share if you face any similar issues, during the implementation.  Kindly throw some light on this issue.

 

Log Snippet:

03-10 17:42:31.482 18173 18182 D MailTransport: *** IMAP open demo.isode.com:143

 

03-10 17:42:32.072 18173 18182 D MailTransport: >>> 1 CAPABILITY

03-10 17:42:32.392 18173 18182 D Email   : <<< #null# ["CAPABILITY", "IMAP4rev1", "UIDPLUS", "LITERAL+", "UNSELECT", "NAMESPACE", "SORT", "BINARY", "MULTIAPPEND", "THREAD=ORDEREDSUBJECT", "THREAD=REFERENCES", "ESEARCH", "LIST-EXTENDED", "IDLE", "URLAUTH", "CATENATE", "CONDSTORE", "QRESYNC", "ENABLE", "STARTTLS", "ACL", "RIGHTS=kxet", "QUOTA", "COMPRESS=DEFLATE", "SASL-IR", "WITHIN", "CONTEXT=SEARCH", "SEARCHRES", "SPECIAL-USE", "MOVE", "AUTH=SCRAM-SHA-1", "AUTH=DIGEST-MD5", "AUTH=CRAM-MD5", "AUTH=PLAIN"]

03-10 17:42:32.472 18173 18182 D Email   : <<< #1# ["OK", "CAPABILITY Completed"]

 

03-10 17:42:32.492 18173 18182 D MailTransport: >>> 2 AUTHENTICATE DIGEST-MD5

……………………….

 

03-10 17:42:33.222 18173 18182 D MailTransport: >>> 3 COMPRESS DEFLATE

03-10 17:42:33.352 18173 18182 D Email   : <<< #3# ["OK", "Compression active"]

 

03-10 17:42:33.392 18173 18182 D MailTransport: >>> 4 NAMESPACE

03-10 17:42:33.412 18173 18182 D IMAPSocketOutputStream: RawBytes >>78 9C

03-10 17:42:33.422 18173 18182 D IMAPSocketOutputStream: RawBytes >>120

03-10 17:42:33.462 18173 18182 D IMAPSocketOutputStream: RawBytes >>-100

 

03-10 17:42:33.532 18173 18182 D ImapResponseParser: parseResponse

03-10 17:42:33.552 18173 18182 D IMAPSocketInputStream: read

 

Regards,

Jay

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Arnt Gulbrandsen | 3 Mar 19:46 2015
Picon

create-special-use

Hi,

do any servers implement that? If so, which?

Some Gmail-specific clients create an x-gm-label called Later. I don't see 
a way to do anything equivalent using create-special-use, am I overlooking 
anything?

Arnt

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Jayantheesh S B | 27 Feb 21:57 2015

The IMAP APPENDLIMIT Extension - version 04

Hi All,

 

Please find the next version (04) of the draft attached with review comments addressed.

 

Changes in this version:

1.       Append-limit-value changed from 32 bits to 64 bits unsigned number

 

Regards,

Jay

INTERNET-DRAFT                                           Jayantheesh S B 
Intended status: Standards Track                                 Samsung
Expires: August 2015                                Narendra Singh Bisht
                                                                 Samsung
                                                       February 27, 2015

                      The IMAP APPENDLIMIT Extension
                draft-jayantheesh-imap-appendlimit-extension-04

Abstract

This memo defines an extension to the IMAP service whereby a server can
advertise its capability, to support maximum mail upload size using
CAPABILITY, SELECT/EXAMINE and LIST command.

Status of this Memo

This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. This document may not be modified, and
derivative works of it may not be created, except to publish it as an
RFC and to translate it into languages other than English.

Internet-Drafts are working documents of the Internet Engineering Task
Force (IETF), its areas, and its working groups.  Note that other groups
may also distribute working documents as Internet-Drafts.

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

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

The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html

This Internet-Draft will expire on August, 2015.

Copyright Notice

Copyright (c) 2014 IETF Trust and the persons identified as the
document authors.  All rights reserved.

This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document.  Please review these documents carefully,
as they describe your rights and restrictions with respect to this
document.

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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  2
     1.1. Conventions and Terminology . . . . . . . . . .  . . . . .   2
   2. APPENDLIMIT Extension . . . . . . . . . . . . . . . . . . . . .  2
   3. Mailbox specific APPENDLIMIT . . . . . . . . . . . . . . . . . . 3
     3.1. SELECT response . . . . . . . . . . . . . . . . . . . . . .  4
     3.2. LIST response . . . . . . . . . . . . . . . . . . . . . . .  4
   4. APPEND response . . . . . . . . . . . . . . . . . . . . . . . .  5
   5. Formal syntax . . . . . . . . . . . . . . . . . . . . . . . . .  5
   6. Security Considerations  . . . . . . . . . . . . . . . . . . . . 6
   7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . .  6
   8. References . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
    8.1 Normative References . . . . . . . . . . . . . . . . . . . . . 6
    8.2 Informative References . . . . . . . . . . . . . . . . . . . . 7
   9. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . .  7
   10. Author's Address . .. . . . . . . . . . . . . . . . . . . . . . 7

1. Introduction

Several IMAP server have limitation for mail upload size which is not
published to the email client.  When email client APPEND a mail with
huge attachments, it fails due to size restriction set by the IMAP
server.  This results in unnecessary resource usage.  Especially in the 
mobile device environment, appending mail with huge attachment consumes
device resources like device battery power and mobile data.

The IMAP APPENDLIMIT extension provides an ability to advertise maximum
upload size allowed by the IMAP server, so that email client knows the
size limitation beforehand.

1.1. Conventions and Terminology

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL 
NOT","SHOULD", "SHOULD NOT", "RECOMMENDED",  "MAY", and "OPTIONAL" in
this document are to be interpreted as described in RFC 2119.

Example lines prefaced by "C:" are sent by the client and ones prefaced
by "S:" by the server.  The five characters [...] means that something
has been elided.

2. APPENDLIMIT Extension

An IMAP server that supports APPENDLIMIT advertises this by including
the word APPENDLIMIT in its capability list.  IMAP server shall publish
the supported mail upload size as part of CAPABILITY response.  The

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advertised upload limit is common across the mailboxes, but client
can still issue SELECT/EXAMINE or LIST command to get the mailbox
specific upload limit set by the IMAP server.  In this case,
APPENDLIMIT value obtained as part of SELECT/EXAMINE or LIST command
takes precedence over the value returned as part of CAPABILITY
response.

The following example, demonstrates the APPENDLIMIT capability with
mailbox limit.

C: t1 CAPABILITY
S: * CAPABILITY IMAP4rev1 ID APPENDLIMIT=257890
S: t1 OK foo

If APPENDLIMIT value is omitted in CAPABILITY response, then client
SHOULD issue SELECT/EXAMINE or LIST command to get the mailbox specific
limit set by the server.  New response code APPENDLIMIT is added to get
the mailbox specific limit.  Refer section 5 for response code syntax.

The following example demonstrates, its usage.

C: t1 CAPABILITY
S: * CAPABILITY IMAP4rev1 ID APPENDLIMIT
S: t1 OK foo

C: t2 SELECT INBOX
S: * 172 EXISTS
S: * OK [APPENDLIMIT 257890] Maximum upload limit
S: * OK [UIDVALIDITY 3857529045] UIDs valid
S: * FLAGS (\Answered \Flagged \Deleted \Seen \Draft)
S: * OK [PERMANENTFLAGS (\Deleted \Seen \*)] Limited
S: t2 OK [READ-WRITE] SELECT completed

By looking at the upload size restriction set by the IMAP server, client
MUST not try to upload mail more than advertised limit in the APPEND
command. 

3. Mailbox specific APPENDLIMIT

IMAP server can still have mailbox specific APPENDLIMIT restriction,
which may not be advertised as part of CAPABILITY response.  In this
case, client can issue SELECT/EXAMINE command to get the per mailbox
specific limit set by the server.  Similarly, if client wish to know
the mailbox specific limit in authenticated state, can be done by
issuing the LIST command in combination with STATUS command.

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3.1 SELECT response

Client can get the per mailbox append limit by issuing the SELECT/
EXAMINE command.  APPENDLIMIT size to this mailbox is obtained as part
of untagged OK response.  In this case, this APPENDLIMIT value will
supersede the value received as part of CAPABILITY response.  If no
per-mailbox APPENDLIMIT is specified for a folder, but the server did
specify a common APPENDLIMIT in the CAPABILITY response, then the
common APPENDLIMIT applies to that folder.

C: t2 SELECT INBOX
S: * 172 EXISTS
S: * OK [APPENDLIMIT 257890] Maximum upload limit
S: [...]
S: t2 OK [READ-WRITE] SELECT completed

In the above example, APPENDLIMIT represents the maximum upload size for
this mailbox.

OK [APPENDLIMIT <n>] Maximum upload limit for this mailbox, in bytes.
                     Refer to section 5 for more information.  If this
                     is missing, the client can always honour the
                     value received as part of CAPABILITY response.

3.2 LIST response

IMAP client can get the mailbox specific APPENDLIMIT in authenticated
state, where it do not need to issue SELECT/EXAMINE command.  LIST
command in combination with STATUS command can be issued to get the per
mailbox specific APPENDLIMIT set by the server.  Refer RFC 5819 for the
usage of LIST command in combination with STATUS command.  Note that a
server implementing this extension, is syntactically compatible with
RFC 5819, however support for RFC 5258 or RFC 5819 is not required,
when implementing this extension.

The following example demonstrates, its usage.

C: t1 LIST "" % RETURN (STATUS (APPENDLIMIT))
S: * LIST () "."  "INBOX"
S: * STATUS "INBOX" (APPENDLIMIT 257890)
S: t1 OK List completed.

New attribute APPENDLIMIT is added to get the limit set by the server
for this mailbox as part of STATUS command.  The STATUS response occurs
as a result of an STATUS command.  It returns the mailbox name that

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matches the STATUS specification and the requested mailbox status
information.  IMAP server should recognize an extra "RETURN (STATUS
 (APPENDLIMIT))" at the end of a LIST command and emit an extra STATUS
response for each matching mailbox.  Refer to section 5 for the syntax.

Invoking STATUS command with APPENDLIMIT is also acceptable.  Below
example demonstrates, its usage.

C: t1 STATUS INBOX (APPENDLIMIT)
S: * STATUS INBOX (APPENDLIMIT 257890)
S: t1 OK STATUS completed

4. APPEND response

If client uploads a mail which exceeds the maximum upload size set
to that mailbox, then server SHALL reject the APPEND command with a
tagged TOOBIG response code.  Refer RFC 4469 Section (4) for various
APPEND response codes and its handling.

Client can avoid use of LITERAL+, when maximum upload size
supported by the IMAP server is unknown. 

5. Formal syntax

The following syntax specification uses the Augmented Backus-Naur
Form (ABNF) notation as specified in [RFC5234] including the core
rules in Appendix B.1.  [RFC3501] defines the non-terminals
"capability", "resp-text-code" and "status-att".
Except as noted otherwise, all alphabetic characters are case-
insensitive.  The use of upper or lower case characters to define
token strings is for editorial clarity only.  Implementations MUST
accept these strings in a case-insensitive fashion.

appendlimit-cap = "APPENDLIMIT" ["=" append-limit-value]
capability /= appendlimit-cap

appendlimit-respcode = "APPENDLIMIT" SP append-limit-value
resp-text-code /= appendlimit-respcode

append-limit-value = 1*DIGIT
                     ; Unsigned 64-bit integer
                     ; (0 <= n < 18,446,744,073,709,551,615)

appendlimit-status-att = "APPENDLIMIT"
status-att /=appendlimit-status-att

A number indicating the fixed maximum message size in bytes that the
server will accept.  APPENDLIMIT=0 indicates the server SHALL not
Jayantheesh & Narendra     Expires August, 2015              [Page 5]

Internet-Draft               IMAP APPENDLIMIT           February 2015

accept APPEND command due to size restriction.  The syntax of the
parameter follows the augmented BNF notation of [RFC5234].  If this
capability is omitted, no information is conveyed about the server's
fixed maximum mail upload size.

6. Security Consideration

It is believed that this extension doesn't add any new security
considerations that are not already present in the base IMAP
protocol [RFC3501].

7. IANA Considerations

The IANA is requested to add APPENDLIMIT to the IMAP4 Capabilities
Registry.  [[Note to RFC-editor: please remove the following before
publication: This registration should take place at the following
location: http://www.iana.org/assignments/imap4-capabilities]]

8. References

8.1 Normative References

The following documents contain definitions or specifications that
are necessary to understand this document properly

[RFC2119]  Bradner, "Key words for use in RFCs to Indicate
           Requirement Levels", RFC 2119, Harvard University, March
           1997.

[RFC3501]  Crispin, "INTERNET MESSAGE ACCESS PROTOCOL - VERSION 4rev1",
           University of Washington, March 2003

[RFC5234]  Crocker, Overell, "Augmented BNF for Syntax
           Specifications: ABNF", RFC 5234, Brandenburg
           Internetworking, Demon Internet Ltd, January 2008

[RFC5322]  P. Resnick, Ed, "Internet Message Format", RFC 5322,
           Qualcomm Incorporated, October 2008

[RFC2088]  J. Myers, Carnegie Mellon, "IMAP4 non-synchronizing
           literals",  January 1997
		   
[RFC4469]  P. Resnick, "Internet Message Access Protocol (IMAP)
           CATENATE Extension",  April 2006
		   
[RFC5819]  A. Melnikov, T. Sirainen, "IMAP4 Extension for Returning
           STATUS Information in Extended LIST",  March 2010
		   
Jayantheesh & Narendra     Expires August, 2015               [Page 6]

Internet-Draft               IMAP APPENDLIMIT            February 2015

[RFC5258]  A. Melnikov, B. Leiba, "Internet Message Access Protocol
           version 4 - LIST Command Extensions",  March 2010
		   
8. 2 Informative References

The following documents describe related protocols:

[RFC2087]  Myers, J., "IMAP4 QUOTA extension", RFC 2087,
           January 1997

[RFC7377]  B. Leiba, A. Melnikov, "IMAP4 Multimailbox SEARCH
           Extension", RFC 7377, October 2014

9. Acknowledgement

TBD

10. Author's Address

Jayantheesh S B
Samsung Telecommunications America,
685 US Highway 202/206,
Bridgewater, NJ 08807.
USA
Email: jayantheesh.sb <at> gmail.com

Narendra Singh Bisht
Samsung Telecommunications America,
685 US Highway 202/206,
Bridgewater, NJ 08807.
USA
Email: narendrasingh.bisht <at> gmail.com

Jayantheesh & Narendra     Expires August, 2015               [Page 7]
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Jayantheesh S B | 18 Feb 21:05 2015

IMAP Idle for Multiple folders

Dear All,

 

As part of IMAP IDLE connection (https://tools.ietf.org/html/rfc2177) any changes like EXISTS, EXPUNGE, FETCH to one particular mailbox can be pushed to IMAP client.

 

But in case, if IMAP client want to receive notification for multiple folders then multiple IMAP connection has to be opened.

 

Is there a way to receive updates for multiple folders in same IMAP connection ? Please share your thoughts.

Regards,

Jay

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Jayantheesh S B | 5 Jan 18:50 2015

Re: The IMAP APPENDLIMIT Extension

Hi Pete,

Thanks for your review comments. 

Please find my comments inline. 

Regards,
Jay

-----Original Message-----
From: Pete Maclean [mailto:groups <at> maclean.com] 
Sent: Saturday, January 03, 2015 8:11 AM
To: Jayantheesh S B; 'imapext <at> ietf.org'
Subject: Re: [imapext] The IMAP APPENDLIMIT Extension

Jay,

I have not said anything on APPENDLIMIT before but, reading your latest draft now, there are a few things I
wonder about.  I don't think any of these necessarily requires any changes to the draft but some may merit
additional consideration.

In section 5 you make reference to "the server's fixed maximum mail upload size".  What is the intended scope
of said fixedness.  Should a client assume that a maximum upload size obtained in one session applies in a
later session?  I think it should not.  Hardware or other changes at the server could surely lead to a maximum
upload size changing over time.

[Jay] Upload size obtained using SELECT/EXAMINE always overrides the CAPABILITY response. So, maximum
upload size obtained in one session does not apply for another session.

How should a client behave if it obtains a maximum upload size for a given mailbox in a LIST command and then
later in the same session it does a SELECT/EXAMINE for the same mailbox that quotes a different maximum
upload size?  For that matter, is it valid for a server to return different maximum upload sizes in
CAPABILITY responses within a single session?  In cases where a maximum upload size is dependent on a
quota, it could make sense for these things to happen.

Surely it would be very valuable to include in this extension a means for a server to indicate that it does not
accept APPENDs at all.  For IMAP servers fronting email archives, it is entirely reasonable for APPENDs to
be unsupported.  In other cases, it seems reasonable for APPENDs to be disallowed for certain mailboxes
(as, for example, in a proxy situation or when a mailbox reaches maximum capacity).  An easy way to deal with
this would perhaps be to change the syntax to allow an append limit of 0 with the meaning, not that
zero-length messages may be APPENDed (something that my checks show that many servers disallow anyway),
but that APPENDs are not allowed period.  This could avoid a lot of trouble, I believe.

[Jay] This is the good idea. I will change the next version of the draft to accept the APPENDLIMIT=0,
indicates the server will not accept any APPEND command due to size restriction.

Pete Maclean

At 05:12 PM 12/19/2014, Jayantheesh S B wrote:
>Hi All,
>
>Please find the next version of the draft attached with all the review 
>comments addressed.
>
>If you have any comments/suggestions in the attached version, kindly share it.
>
>Regards,
>Jay
>
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Alexey Melnikov | 4 Jan 19:17 2015

Re: The IMAP APPENDLIMIT Extension

Hi Pete,

On 03/01/2015 13:11, Pete Maclean wrote:
> Jay,
>
> I have not said anything on APPENDLIMIT before but, reading your 
> latest draft now, there are a few things I wonder about.  I don't 
> think any of these necessarily requires any changes to the draft but 
> some may merit additional consideration.
>
> In section 5 you make reference to "the server's fixed maximum mail 
> upload size".  What is the intended scope of said fixedness. Should a 
> client assume that a maximum upload size obtained in one session 
> applies in a later session?  I think it should not.
I don't think this matters, because the limit would be always advertised 
in CAPABILITY response and/or on SELECT anyway.
> Hardware or other changes at the server could surely lead to a maximum 
> upload size changing over time.
>
> How should a client behave if it obtains a maximum upload size for a 
> given mailbox in a LIST command and then later in the same session it 
> does a SELECT/EXAMINE for the same mailbox that quotes a different 
> maximum upload size?  For that matter, is it valid for a server to 
> return different maximum upload sizes in CAPABILITY responses within a 
> single session?  In cases where a maximum upload size is dependent on 
> a quota, it could make sense for these things to happen.
Yes, it is probably sensible to allow for that.
> Surely it would be very valuable to include in this extension a means 
> for a server to indicate that it does not accept APPENDs at all.
APPENDLIMIT=0?
> For IMAP servers fronting email archives, it is entirely reasonable 
> for APPENDs to be unsupported.  In other cases, it seems reasonable 
> for APPENDs to be disallowed for certain mailboxes (as, for example, 
> in a proxy situation or when a mailbox reaches maximum capacity).  An 
> easy way to deal with this would perhaps be to change the syntax to 
> allow an append limit of 0 with the meaning, not that zero-length 
> messages may be APPENDed (something that my checks show that many 
> servers disallow anyway), but that APPENDs are not allowed period.  
> This could avoid a lot of trouble, I believe.
Yes, I think this is a good idea.

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Pete Maclean | 3 Jan 14:11 2015

Re: The IMAP APPENDLIMIT Extension

Jay,

I have not said anything on APPENDLIMIT before but, reading your 
latest draft now, there are a few things I wonder about.  I don't 
think any of these necessarily requires any changes to the draft but 
some may merit additional consideration.

In section 5 you make reference to "the server's fixed maximum mail 
upload size".  What is the intended scope of said fixedness.  Should 
a client assume that a maximum upload size obtained in one session 
applies in a later session?  I think it should not.  Hardware or 
other changes at the server could surely lead to a maximum upload 
size changing over time.

How should a client behave if it obtains a maximum upload size for a 
given mailbox in a LIST command and then later in the same session it 
does a SELECT/EXAMINE for the same mailbox that quotes a different 
maximum upload size?  For that matter, is it valid for a server to 
return different maximum upload sizes in CAPABILITY responses within 
a single session?  In cases where a maximum upload size is dependent 
on a quota, it could make sense for these things to happen.

Surely it would be very valuable to include in this extension a means 
for a server to indicate that it does not accept APPENDs at all.  For 
IMAP servers fronting email archives, it is entirely reasonable for 
APPENDs to be unsupported.  In other cases, it seems reasonable for 
APPENDs to be disallowed for certain mailboxes (as, for example, in a 
proxy situation or when a mailbox reaches maximum capacity).  An easy 
way to deal with this would perhaps be to change the syntax to allow 
an append limit of 0 with the meaning, not that zero-length messages 
may be APPENDed (something that my checks show that many servers 
disallow anyway), but that APPENDs are not allowed period.  This 
could avoid a lot of trouble, I believe.

Pete Maclean

At 05:12 PM 12/19/2014, Jayantheesh S B wrote:
>Hi All,
>
>Please find the next version of the draft attached with all the 
>review comments addressed.
>
>If you have any comments/suggestions in the attached version, kindly share it.
>
>Regards,
>Jay
>
>_______________________________________________
>imapext mailing list
>imapext <at> ietf.org
>https://www.ietf.org/mailman/listinfo/imapext

_______________________________________________
imapext mailing list
imapext <at> ietf.org
https://www.ietf.org/mailman/listinfo/imapext

Jayantheesh S B | 19 Dec 23:12 2014

The IMAP APPENDLIMIT Extension

Hi All,

 

Please find the next version of the draft attached with all the review comments addressed.

 

If you have any comments/suggestions in the attached version, kindly share it.

 

Regards,

Jay

INTERNET-DRAFT                                           Jayantheesh S B 
Intended status: Standards Track                                 Samsung
Expires: June 2015                                  Narendra Singh Bisht
                                                                 Samsung
                                                       December 19, 2014

                      The IMAP APPENDLIMIT Extension
                draft-jayantheesh-imap-appendlimit-extension-02

Abstract

This memo defines an extension to the IMAP service whereby a server can
advertise its capability, to support maximum mail upload size using
CAPABILITY, SELECT/EXAMINE and LIST command.

Status of this Memo

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This document is subject to BCP 78 and the IETF Trust's Legal
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document.

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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  2
     1.1. Conventions and Terminology . . . . . . . . . .  . . . . .   2
   2. APPENDLIMIT Extension . . . . . . . . . . . . . . . . . . . . .  2
   3. Mailbox specific APPENDLIMIT . . . . . . . . . . . . . . . . . . 3
     3.1. SELECT response . . . . . . . . . . . . . . . . . . . . . .  4
     3.2. LIST response . . . . . . . . . . . . . . . . . . . . . . .  4
   4. APPEND response . . . . . . . . . . . . . . . . . . . . . . . .  5
   5. Formal syntax . . . . . . . . . . . . . . . . . . . . . . . . .  5
   6. Security Considerations  . . . . . . . . . . . . . . . . . . . . 6
   7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . .  6
   8. References . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
    8.1 Normative References . . . . . . . . . . . . . . . . . . . . . 6
    8.2 Informative References . . . . . . . . . . . . . . . . . . . . 7
   9. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . .  7
   10. Author's Address . .. . . . . . . . . . . . . . . . . . . . . . 7

1. Introduction

Several IMAP server have limitation for mail upload size which is not
published to the email client.  When email client APPEND a mail with
huge attachments, it fails due to size restriction set by the IMAP
server.  This results in unnecessary resource usage.  Especially in the 
mobile device environment, appending mail with huge attachment consumes
device resources like device battery power and mobile data.

The IMAP APPENDLIMIT extension provides an ability to advertise maximum
upload size allowed by the IMAP server, so that email client knows the
size limitation beforehand.

1.1. Conventions and Terminology

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL 
NOT","SHOULD", "SHOULD NOT", "RECOMMENDED",  "MAY", and "OPTIONAL" in
this document are to be interpreted as described in RFC 2119.

Example lines prefaced by "C:" are sent by the client and ones prefaced
by "S:" by the server.  The five characters [...] means that something
has been elided.

2. APPENDLIMIT Extension

An IMAP server that supports APPENDLIMIT advertises this by including
the word APPENDLIMIT in its capability list.  IMAP server shall publish
the supported mail upload size as part of CAPABILITY response.  The

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advertised upload limit is common across the mailboxes, but client
can still issue SELECT/EXAMINE or LIST command to get the mailbox
specific upload limit set by the IMAP server.  In this case,
APPENDLIMIT value obtained as part of SELECT/EXAMINE or LIST command
takes precedence over the value returned as part of CAPABILITY
response.

The following example, demonstrates the APPENDLIMIT capability with
mailbox limit.

C: t1 CAPABILITY
S: * CAPABILITY IMAP4rev1 ID APPENDLIMIT=257890
S: t1 OK foo

If APPENDLIMIT value is omitted in CAPABILITY response, then client
SHOULD issue SELECT/EXAMINE or LIST command to get the mailbox specific
limit set by the server.  New response code APPENDLIMIT is added to get
the mailbox specific limit.  Refer section 5 for response code syntax.

The following example demonstrates, its usage.

C: t1 CAPABILITY
S: * CAPABILITY IMAP4rev1 ID APPENDLIMIT
S: t1 OK foo

C: t2 SELECT INBOX
S: * 172 EXISTS
S: * OK [APPENDLIMIT 257890] Maximum upload limit
S: * OK [UIDVALIDITY 3857529045] UIDs valid
S: * FLAGS (\Answered \Flagged \Deleted \Seen \Draft)
S: * OK [PERMANENTFLAGS (\Deleted \Seen \*)] Limited
S: t2 OK [READ-WRITE] SELECT completed

By looking at the upload size restriction set by the IMAP server, client
MUST not try to upload mail more than advertised limit in the APPEND
command. 

3. Mailbox specific APPENDLIMIT

IMAP server can still have mailbox specific APPENDLIMIT restriction,
which may not be advertised as part of CAPABILITY response.  In this
case, client can issue SELECT/EXAMINE command to get the per mailbox
specific limit set by the server.  Similarly, if client wish to know
the mailbox specific limit in authenticated state, can be done by
issuing the LIST command in combination with STATUS command.

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3.1 SELECT response

Client can get the per mailbox append limit by issuing the SELECT/
EXAMINE command.  APPENDLIMIT size to this mailbox is obtained as part
of untagged OK response.  In this case, this APPENDLIMIT value will
supersede the value received as part of CAPABILITY response.  If no
per-mailbox APPENDLIMIT is specified for a folder, but the server did
specify a common APPENDLIMIT in the CAPABILITY response, then the
common APPENDLIMIT applies to that folder.

C: t2 SELECT INBOX
S: * 172 EXISTS
S: * OK [APPENDLIMIT 257890] Maximum upload limit
S: [...]
S: t2 OK [READ-WRITE] SELECT completed

In the above example, APPENDLIMIT represents the maximum upload size for
this mailbox.

OK [APPENDLIMIT <n>] Maximum upload limit for this mailbox, in bytes.
                     Refer to section 5 for more information.  If this
                     is missing, the client can always honour the
                     value received as part of CAPABILITY response.

3.2 LIST response

IMAP client can get the mailbox specific APPENDLIMIT in authenticated
state, where it do not need to issue SELECT/EXAMINE command.  LIST
command in combination with STATUS command can be issued to get the per
mailbox specific APPENDLIMIT set by the server.  Refer RFC 5819 for the
usage of LIST command in combination with STATUS command.  Note that a
server implementing this extension, is syntactically compatible with
RFC 5819, however support for RFC 5258 or RFC 5819 is not required,
when implementing this extension.

The following example demonstrates, its usage.

C: t1 LIST "" % RETURN (STATUS (APPENDLIMIT))
S: * LIST () "."  "INBOX"
S: * STATUS "INBOX" (APPENDLIMIT 257890)
S: t1 OK List completed.

New attribute APPENDLIMIT is added to get the limit set by the server
for this mailbox as part of STATUS command.  The STATUS response occurs
as a result of an STATUS command.  It returns the mailbox name that

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matches the STATUS specification and the requested mailbox status
information.  IMAP server should recognize an extra "RETURN (STATUS
 (APPENDLIMIT))" at the end of a LIST command and emit an extra STATUS
response for each matching mailbox.  Refer to section 5 for the syntax.

Invoking STATUS command with APPENDLIMIT is also acceptable.  Below
example demonstrates, its usage.

C: t1 STATUS INBOX (APPENDLIMIT)
S: * STATUS INBOX (APPENDLIMIT 257890)
S: t1 OK STATUS completed

4. APPEND response

If client uploads a mail which exceeds the maximum upload size set
to that mailbox, then server SHALL reject the APPEND command with a
tagged TOOBIG response code.  Refer RFC 4469 Section (4) for various
APPEND response codes and its handling.

Client can avoid use of LITERAL+, when maximum upload size
supported by the IMAP server is unknown. 

5. Formal syntax

The following syntax specification uses the Augmented Backus-Naur
Form (ABNF) notation as specified in [RFC5234] including the core
rules in Appendix B.1.  [RFC3501] defines the non-terminals
"capability", "resp-text-code" and "status-att".
Except as noted otherwise, all alphabetic characters are case-
insensitive.  The use of upper or lower case characters to define
token strings is for editorial clarity only.  Implementations MUST
accept these strings in a case-insensitive fashion.

appendlimit-cap = "APPENDLIMIT" ["=" nz-number]
capability /= appendlimit-cap

appendlimit-respcode = "APPENDLIMIT" SP nz-number
resp-text-code /= appendlimit-respcode

appendlimit-status-att = "APPENDLIMIT"
status-att /=appendlimit-status-att

A non-zero number indicating the fixed maximum message size in bytes
that the server will accept.  The syntax of the parameter follows the
augmented BNF notation of [RFC5234].  If this capability is
omitted, no information is conveyed about the server's fixed maximum
mail upload size.

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6. Security Consideration

It is believed that this extension doesn't add any new security
considerations that are not already present in the base IMAP
protocol [RFC3501].

7. IANA Considerations

The IANA is requested to add APPENDLIMIT to the IMAP4 Capabilities
Registry.  [[Note to RFC-editor: please remove the following before
publication: This registration should take place at the following
location: http://www.iana.org/assignments/imap4-capabilities]]

8. References

8.1 Normative References

The following documents contain definitions or specifications that
are necessary to understand this document properly

[RFC2119]  Bradner, "Key words for use in RFCs to Indicate
           Requirement Levels", RFC 2119, Harvard University, March
           1997.

[RFC3501]  Crispin, "INTERNET MESSAGE ACCESS PROTOCOL - VERSION 4rev1",
           University of Washington, March 2003

[RFC5234]  Crocker, Overell, "Augmented BNF for Syntax
           Specifications: ABNF", RFC 5234, Brandenburg
           Internetworking, Demon Internet Ltd, January 2008

[RFC5322]  P. Resnick, Ed, "Internet Message Format", RFC 5322,
           Qualcomm Incorporated, October 2008

[RFC2088]  J. Myers, Carnegie Mellon, "IMAP4 non-synchronizing
           literals",  January 1997
		   
[RFC4469]  P. Resnick, "Internet Message Access Protocol (IMAP)
           CATENATE Extension",  April 2006
		   
[RFC5819]  A. Melnikov, T. Sirainen, "IMAP4 Extension for Returning
           STATUS Information in Extended LIST",  March 2010
		   
[RFC5258]  A. Melnikov, B. Leiba, "Internet Message Access Protocol
           version 4 - LIST Command Extensions",  March 2010

		   
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8. 2 Informative References

The following documents describe related protocols:

[RFC2087]  Myers, J., "IMAP4 QUOTA extension", RFC 2087,
           January 1997

[RFC7377]  B. Leiba, A. Melnikov, "IMAP4 Multimailbox SEARCH
           Extension", RFC 7377, October 2014

9. Acknowledgement

TBD

10. Author's Address

Jayantheesh S B
Samsung Telecommunications America,
685 US Highway 202/206,
Bridgewater, NJ 08807.
USA
Email: jayantheesh.sb <at> gmail.com

Narendra Singh Bisht
Samsung Telecommunications America,
685 US Highway 202/206,
Bridgewater, NJ 08807.
USA
Email: narendrasingh.bisht <at> gmail.com

	
	
	
	

	
	
	
	
	
	
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