Network Working Group D. Cridland
Internet-Draft Clues
Expires: February 18, 2003 A. Melnikov
ACI
August 20, 2002
IMAP4rev1 QUOTA Extension
draft-cridland-imap-quota-00
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
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Copyright Notice
Copyright (C) The Internet Society (2002). All Rights Reserved.
Abstract
The QUOTA extension of the Internet Message Access Protocol IMAP4 [2]
permits administrative limits on resource usage (quotas) to be
manipulated through the IMAP protocol.
This memo replaces RFC2087 [4], but attempts to remain backwards
compatible whenever possible.
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1. Document Conventions
In protocol examples, this document uses a prefix of "C: " to denote
lines sent by the client to the server, and "S: " for lines sent by
the server to the client. Lines prefixed with "// " are comments
explaining the previous protocol line. These prefixes and comments
are not part of the protocol. Lines without any of these prefixes
are continuations of the previous line, and no line break is present
in the protocol unless specifically mentioned.
Again, for examples, the hierarchy separator on the server is
presumed to be "/" throughout. None of these assumptions is required
nor recommended by this memo.
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 RFC2119 [5].
Other capitalised words are IMAP4 [2] keywords or keywords from this
document.
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2. Introduction and Overview
The QUOTA extension is present in any IMAP4rev1 server which
advertises any CAPABILITY beginning with "QUOTA=".
The capability "QUOTA", with no "=", denotes a RFC2087 [4] compliant
server. Some commands and responses are not present in such servers,
and clients MUST NOT rely on their presence in the absence of any
capability beginning "QUOTA=".
Quotas can be used to restrict clients for administrative reasons,
but the QUOTA extension can also be used to indicate system limits
and current usage levels to clients.
Although RFC2087 [4] specified an IMAP4 QUOTA extension, and this has
seen deployment in servers, it has seen little deployment in clients.
Since the meaning of the resources was left implementation-dependant,
it was impossible for a client implementation to determine which
resources were supported, and impossible to determine which mailboxes
were in a given quota root, without a priori knowledge of the
implementation.
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3. Terms
3.1 Resource
A resource has a name, a formal definition.
3.1.1 Name
The resource name is an atom, as defined in IMAP4 [2]. These MUST be
registered with IANA, or begin with "X-", which indicates an
experimental resource. Implementation specific resources MUST be
registered with IANA, and begin with "V-".
Supported resource names MUST be advertised as a capability, by
prepending the resource name with "QUOTA=RES-". Server is not
required to support all reported resource types on all quota roots.
3.1.2 Definition
The resource definition or document containing it, while not visible
through the protocol, SHOULD be registered with IANA.
The usage of a resource MUST be represented as a 32 bit unsigned
integer. 0 indicates no usage of a resource. Usage integers MUST
NOT represent proportional use, such that a client can compare
available resource between two separate quota roots or servers with
reasonable accuracy.
Limits will be specified as, and MUST be represented as, an integer.
0 indicates that any usage is prohibited.
Limits may be hard or soft - that is, an implementation MAY choose,
or be configured, to disallow any command if the limit on a resource
is or would be exceeded.
All resources which the server handles must be advertised in a
CAPABILITY constisting of the resource name prefixed by "QUOTA=RES-".
For compatability with RFC2087 [4], a client which discovers
resources available on the server which are not advertised through
this mechanism MUST treat the resource as if it were completely
opaque, and without any meaning.
The resources STORAGE (Section 5.1), MESSAGES (Section 5.2) and
MAILBOXES (Section 5.3) are defined in this memo.
3.2 Quota Root
Each mailbox has zero or more implementation-defined named "quota
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roots". Each quota root has zero or more resource limits (quotas).
All mailboxes that share the same named quota root share the resource
limits of the quota root.
Quota root names need not be mailbox names, nor is there any
relationship defined by this memo between a Quota root name and a
mailbox name. A quota root name is an astring, as defined in IMAP4
[2]. It MUST be treated as an opaque string by any clients which do
not have a priori knowledge of the server implementation.
Quota roots are used since not all implementations may be able to
calculate usage, or apply quotas, on arbitary mailboxes or mailbox
hierarchies. A client might be able to determine how a quota root
relates to the mailboxes it governs by looking at any mapping which
MAY be given in a QUOTAMAP (Section 4.2.3) response.
Not all resources may be limitable or calculatable for all quota
roots. Further, not all resources may support all limits - some
limits may be present in the underlying system. A server
implementation of this memo SHOULD advise the client of such inherent
limits, by generating QUOTA (Section 4.2.1) responses and SHOULD
advise the client of which resources are limitable for a particular
quota root. A SETQUOTA (Section 4.1.3) command MAY also round a
quota limit in an implementation dependant way, if the granularity of
the underlying system demands it. A client MUST be prepared for a
SETQUOTA (Section 4.1.3) command to fail if a limit cannot be set.
Implementation Notes
This means that, for example under UNIX, a quota root may have a
MESSAGES (Section 5.2) quota always set due to the number of inodes
available on the filesystem, and similarly STORAGE (Section 5.1) may
be rounded to the nearest block and limited by free filesystem space.
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4. Definitions
4.1 Commands
The following commands exist for manipulation and querying quotas.
4.1.1 GETQUOTA
Arguments: quota root
Responses: REQUIRED untagged responses: QUOTA
OPTIONAL untagged response: SUPPORTEDQUOTARES
Result: OK - getquota completed
NO - getquota error: no such quota root, permission denied
BAD - command unknown or arguments invalid
The GETQUOTA command takes the name of a quota root and returns the
quota root's resource usage and limits in an untagged QUOTA response.
GETQUOTA command MAY also return an untagged SUPPORTEDQUOTARES
response that lists all resource types that can be set on the quota
root. If the SUPPORTEDQUOTARES response is not returned by the
server, this means that all resource types returned in CAPABILITY
response (i.e. all capability items with "QUOTA=RES-" prefix) are
applicable to the quota root.
Example:
S: * CAPABILITY [...] QUOTA QUOTA=RES-STORAGE [...]
[...]
C: G0001 GETQUOTA "!partition/sda4"
S: * QUOTA "!partition/sda4" (STORAGE 104 10923847)
S: * SUPPORTEDQUOTARES "!partition/sda4" STORAGE
S: G0001 OK Getquota complete
4.1.2 GETQUOTAROOT
Arguments: mailbox name
Responses: REQUIRED untagged responses: QUOTAROOT, QUOTA
OPTIONAL untagged responses: QUOTAMAP
Result: OK - getquotaroot completed
NO - getquotaroot error: no such mailbox, permission denied
BAD - command unknown or arguments invalid
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The GETQUOTAROOT command takes the name of a mailbox and returns the
list of quota roots for the mailbox in an untagged QUOTAROOT
response. For each listed quota root, it also returns the quota
root's resource usage and limits in an untagged QUOTA response and
MAY return an untagged QUOTAMAP response that describes a
relationship between the quota root and the mailbox (mapping).
//Should we remove some information from QUOTAMAP as it is already
returned in QUOTAROOT?
Example:
S: * CAPABILITY [...] QUOTA QUOTA=RES-STORAGE QUOTA=RES-MESSAGES
[...]
[...]
C: G0002 GETQUOTAROOT INBOX
S: * QUOTAROOT INBOX "#user/alice" "!partition/sda4"
S: * QUOTAMAP "#user/alice" INBOX (USER)
S: * QUOTAMAP "!partition/sda4" INBOX ()
S: * QUOTA "#user/alice" (MESSAGES 42 1000)
S: * QUOTA "!partition/sda4" (STORAGE 104 10923847)
S: G0002 OK Getquotaroot complete
4.1.3 SETQUOTA
Arguments: quota root
list of resource limits
Responses: untagged responses: QUOTA
Result: OK - setquota completed
NO - setquota error: can't set that data
BAD - command unknown or arguments invalid
The SETQUOTA command takes the name of a mailbox quota root and a
list of resource limits. The resource limits for the named quota
root are changed to be the specified limits. Any previous resource
limits for the named quota root are discarded.
If the named quota root did not previously exist, an implementation
may optionally create it and change the quota roots for any number of
existing mailboxes in an implementation-defined manner.
// Should we be sending untagged QUOTA responses for all side effect
changes?
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// Quota root name must uniquely identifier mapping [if any]
(different mapping must have non overlapping namespaces)
Example:
S: * CAPABILITY [...] QUOTA QUOTA=RES-STORAGE QUOTA=RES-MESSAGES
[...]
[...]
C: S0000 GETQUOTA "#user/alice"
S: * QUOTA "#user/alice" (STORAGE 54 111 MESSAGES 42 1000)
S: S0000 OK Getquota completed
C: S0001 SETQUOTA "#user/alice" (STORAGE 510)
S: * QUOTA "#user/alice" (STORAGE 58 512)
// The server has rounded the STORAGE quota limit requested to the
nearest 512 blocks of 1024 octects, or else another client has
performed a near simultaneous SETQUOTA, using a limit of 512.
S: S0001 OK Rounded quota
C: S0002 SETQUOTA "!partition/sda4" (STORAGE 99999999)
S: * QUOTA "!partition/sda4" (STORAGE 104 10923847)
// The server has not changed the quota, since this is a
filesystem limit, and cannot be changed. The QUOTA response here
is entirely optional.
S: S0002 NO Cannot change system limit
4.1.4 DELQUOTA
Arguments: quota root
resource name
Responses: no specific responses for this command
Result: OK - delquota completed
NO - delquota error: can't delete that data
BAD - command unknown or arguments invalid
The DELQUOTA command takes the name of a mailbox quota root and a
resource name. The resource limit associated with the resource name
is removed (or reset to the underlying system limit), or other
resources associated with the same quote root are unaffected. (This
command is different from "SETQUOTA <quota_root> (<resource_name>
0)", because the latter discards all resources associated with the
quota root).
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An implementation may optionally change the quota roots for any
number of existing mailboxes in an implementation-defined manner.
// Should we be sending untagged QUOTA responses for all side effect
changes?
Example:
S: * CAPABILITY [...] QUOTA QUOTA=RES-STORAGE QUOTA=RES-MESSAGES
[...]
[...]
C: S0001 DELQUOTA "#user/alice" STORAGE
S: * QUOTA "#user/alice" (MESSAGES 42 1000)
S: S0001 OK STORAGE limit removed.
C: S0002 DELQUOTA "!partition/sda4" STORAGE
S: * QUOTA "!partition/sda4" (STORAGE 104 10923847)
// The server has not changed the quota, since this is a
filesystem limit, and cannot be changed. The QUOTA response here
is entirely optional.
S: S0002 NO Cannot remove system limit
4.1.5 LISTQUOTA
Arguments: quota root
OPTIONAL untagged responses: QUOTAMAP
Result: OK - listquota completed
NO - listquota error: no such quota root, permission denied
BAD - command unknown or arguments invalid
The LISTQUOTA command takes the name of a quota root and returns
QUOTAMAP responses for all mailboxes accessible to the user that are
governed by this quota root
//Client should be prepared to receive a lot of traffic, because this
might be equivalent to performing <LIST "" *>
Example:
S: * CAPABILITY [...] QUOTA QUOTA=RES-STORAGE QUOTA=RES-MESSAGES
[...]
[...]
C: L0001 LISTQUOTA "#user/alice"
S: * QUOTAMAP "#user/alice" INBOX (USER)
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S: * QUOTAMAP "#user/alice" "Drafts" (USER)
S: * QUOTAMAP "#user/alice" "Work/Meetings" (USER)
S: * QUOTAMAP "#user/alice" "Work/Projects" (USER)
S: L0001 OK
4.1.6 STATUS attribute RECOVERABLE
DELETED-MESSAGES and DELETED-STORAGE status data items allow to
estimate the amount of resource freed by an EXPUNGE on a mailbox.
DELETED-MESSAGES status data item requests the server to return the
number of messages with \Deleted flag set.
//DELETED-STORAGE - Is it the sum of RFC822.SIZEs or "How match we
can recover" (depending on messages with \Deleted flag it may be
different)
Example:
S: * CAPABILITY [...] QUOTA QUOTA=RES-STORAGE QUOTA-RES-MESSAGES
[...]
[...]
C: S0003 STATUS INBOX (MESSAGES DELETED-MESSAGES DELETED-STORAGE)
S: * STATUS INBOX (MESSAGES 12 DELETED-MESSAGES 4 DELETED-STORAGE
8)
// 12 messages, 4 of which would be deleted when an EXPUNGE
happens.
S: S0003 OK Status complete.
4.2 Responses
The following responses may be sent by the server.
4.2.1 QUOTA
Data: quota root name
list of resource names, usages, and limits
This response occurs as a result of a GETQUOTA or GETQUOTAROOT
command. The first string is the name of the quota root for which
this quota applies.
The name is followed by a S-expression format list of the resource
usage and limits of the quota root. The list contains zero or more
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triplets. Each triplet contains a resource name, the current usage
of the resource, and the resource limit.
Resources not named in the list are not limited in the quota root.
Thus, an empty list means there are no administrative resource limits
in the quota root.
Example: S: * QUOTA "" (STORAGE 10 512):
4.2.2 QUOTAROOT
Data: mailbox name
zero or more quota root names
This response occurs as a result of a GETQUOTAROOT command. The
first string is the mailbox and the remaining strings are the names
of the quota roots for the mailbox.
Example:
S: * QUOTAROOT INBOX ""
S: * QUOTAROOT comp.mail.mime
4.2.3 QUOTAMAP
Data: quota root name
mailbox name
OPTIONAL mapping name
This response occurs as a result of a GETQUOTAROOT or LISTQUOTA
command. It defines the relationship (mapping) between the quota
root and the mailbox.
4.2.4 SUPPORTEDQUOTARES
Data: quota root name
zero or more resource names
SUPPORTEDQUOTARES response occurs as a result of GETQUOTA command.
It lists all resource types that can be set on the quota root. If
the list of resources is missing (not empty!) this means that the
server can't list supported resources and the client must try
SETQUOTA. Note that SUPPORTEDQUOTARES with no resource name is
different from the absent SUPPORTEDQUOTARES response. If the
SUPPORTEDQUOTARES response is not returned by the server, this means
that all resource types returned in CAPABILITY response (i.e. all
capability items with "QUOTA=RES-" prefix) are applicable to the
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quota root.
4.3 Response Codes
4.3.1 OVERQUOTA
OVERQUOTA response code is returned in NO tagged response to an
APPEND/COPY when the addition of the message(s) puts mailbox over any
one of its quota limits.
Example:
S: C: A003 APPEND Drafts (\Seen $MDNSent) {310}
S: + Ready for literal data
C: Date: Mon, 7 Feb 1994 21:52:25 -0800 (PST)
C: From: Fred Foobar <foobar@Blurdybloop.COM>
C: Subject: afternoon meeting
C: To: mooch@owatagu.siam.edu
C: Message-Id: <B27397-0100000@Blurdybloop.COM>
C: MIME-Version: 1.0
C: Content-Type: TEXT/PLAIN; CHARSET=US-ASCII
C:
C: Hello Joe, do you think we can meet at 3:30 tomorrow?
C:
S: A003 NO [OVERQUOTA] APPEND Failed
4.4 Interaction with the ACL and ACL2 extensions
Both the ACL [3] and ACL2 extensions define access control lists, and
specific permissions which are required for certain actions.
// But how do they interact? Presumably, QUOTAMAP responses
containing mailboxes which cannot be LISTed shouldn't be generated.
Quota Roots which govern no mailboxes to which the client has write
access should also, presumably, be hidden from the client's view?
Administration rights to set quotas?
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5. Resource Definitions
The following resources are defined in this memo. A server
supporting a resource MUST advertise this as a CAPABILITY with a name
consisting of the resource name prefixed by "QUOTA=RES-". A server
MAY support mupltiple resource types, and MUST advertise all
resources it supports.
5.1 STORAGE
The physical space estimate, in units of 1024 octets, of the
mailboxes governed by the quota root. This MAY not be the same as
the sum of the RFC822.SIZE of the messages. Some implementations MAY
include metadata sizes for the messages and mailboxes, other
implementations MAY store messages in such a way that the physical
space used is smaller. Additional messages MAY NOT increase the
usage. Client MUST NOT use the usage figure for anything other than
informational purposes, for example, they MUST NOT refuse to APPEND a
message if the limit less the usage is smaller than the RFC822.SIZE
divided by 1024 of the message.
The usage figure may change as a result of performing actions not
associated with adding new messages to the mailbox, such as SEARCH,
since this may increase the amount of metadata included in the
calculations.
Support for this resource MUST be indicated by the server by
advertising the CAPABILITY "QUOTA=RES-STORAGE".
A resource named the same was also given as an example in RFC2087
[4], clients conformant to this specification connecting to servers
which do not advertise "QUOTA=RES-STORAGE", yet allow a resource
named STORAGE, MUST NOT assume that it is the same resource.
5.2 MESSAGES
The number of messages stored within the mailboxes governed by the
quota root. This MUST be an exact number, however, clients MUST NOT
assume that a change in the usage indicates a change in the number of
messages available, since the quota root may include mailboxes the
client has no access to.
Support for this resource MUST be indicated by the server by
advertising the CAPABILITY "QUOTA=RES-MESSAGES".
A resource named the same was also given as an example in RFC2087
[4], clients conformant to this specification connecting to servers
which do not advertise "QUOTA=RES-MESSAGES", yet allow a resource
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named MESSAGES, MUST NOT assume that it is the same resource.
5.3 MAILBOXES
The number of mailboxes governed by the quota root. This MUST be an
exact number, however, clients MUST NOT assume that a change in the
usage indicates a change in the number of mailboxes, since the quota
root may include mailboxes the client has no access to.
Support for this resource MUST be indicated by the server by
advertising the CAPABILITY "QUOTA=RES-MAILBOXES".
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6. Quota Root Relationship Definitions
Where a specific quota root relationship, or mapping, is given in a
QUOTAMAP response, a client MAY make certain assumptions about which
Quota Root, and therefore which Quota, will govern an existing or
newly created mailbox, without having to use LISTQUOTAROOT after
creation.
Implementations MAY provide no mapping information at all, either for
security reasons or because the mapping actually used does not fit
one of the defined mappings.
Relationship names are atoms, as defined in IMAP4 [2], and must be
registered at IANA. Relationships which are implementation specific
are of limited use for interoperability, however they MUST be
registered and prefixed with "V-", along with the meaning of any
parameters they list.
The mapping applicable to a particular quota root and mailbox is
given in the QUOTAMAP (Section 4.2.3) response.
6.1 HIER
The quota root in question applies to all inferior mailboxes of the
named mailbox, and a newly created inferior mailbox will be governed
by the same quota root.
6.2 SINGLE
The quota root in question applies only to the named mailbox, and to
no other. This is mutually exclusive with HIER mappings.
6.3 USER
The quota root in question applies to all mailboxes owned by the same
user. The definition of ownership is implementation dependant.
// Do we restrict this to the currently logged in user?
6.4 DOMAIN
The quota root in question applies to all mailboxes in the current
domain on at least this server. If the server doesn't support
multiple domains, GLOBAL MUST be used instead.
6.5 GLOBAL
The quota root in question applies to all mailboxes on at least this
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server.
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7. Formal syntax
The following syntax specification uses the Augmented Backus-Naur
Form (ABNF) notation as specified in ABNF [1].
Non-terminals referenced but not defined below are as defined by
IMAP4 [2].
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.
getquota = "GETQUOTA" SP quota_root_name
getquotaroot = "GETQUOTAROOT" SP mailbox
quota_list = "(" quota_resource *(SP quota_resource) ")"
quota_resource = resource_name SP resource_usage SP
resource_limit
quota_response = "QUOTA" SP quota_root_name SP quota_list
quotaroot_response = "QUOTAROOT" SP mailbox *(SP quota_root_name)
setquota = "SETQUOTA" SP quota_root_name SP setquota_list
setquota_list = "(" [setquota_resource *(SP setquota_resource)]
")"
setquota_resource = resource_name SP resource_limit
quota_root_name = astring
resource_limit = number
resource_name = "STORAGE" | "MESSAGES" | "MAILBOXES" |
resource_name_priv | resource_name_vnd | resource_name_ext
resource_name_priv = "X-" atom
;; Private use
resource_name_vnd = "V-" atom
;; Vendor specific, must be registered with IANA
resource_name_ext = atom
;; Not starting with either X- or V- and defined
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;; in a Standard Track or Experimental RFC
resource_names = "(" [resource_name *(SP resource_name)] ")"
resource_usage = number
;; must be less than corresponding resource_limit
quotamap_response = "QUOTAMAP" SP quota_root_name SP mailbox SP "("
[mapping] ")"
suppres_response = "SUPPORTEDQUOTARES" SP quota_root_name [SP
resource_names]
mapping = "HIER" | "SINGLE" | "USER" | "DOMAIN" |
"GLOBAL" | mapping_vendor | mapping_ext
mapping_vendor = "V-" atom
;; Vendor specific, must be registered with IANA
mapping_ext = atom
;; Must be defined by an Experimental or a Standard Track RFC
delquota = "DELQUOTA" SP quota_root_name SP resource_name
capability_quota = capa_quota_res | capa_quota_mapping
capa_quota_res = "QUOTA=RES-" resource_name
capa_quota_mapping?
listquota = "LISTQUOTA" SP quota_root_name
status-att =/ "DELETED-MESSAGES" | "DELETED-STORAGE"
//Should this be optional unless the server implements MESSAGES/
STORAGE?
resp-text-code =/ "OVERQUOTA"
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References
[1] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 2234, November 1997.
[2] Crispin, M., "Internet Message Access Protocol - Version 4rev1",
RFC 2060, December 1996.
[3] Myers, J., "IMAP4 ACL extension", RFC 2086, January 1997.
[4] Myers, J., "IMAP4 QUOTA extension", RFC 2087, January 1997.
[5] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
Authors' Addresses
Dave A. Cridland
Clues Ltd
EMail: dave.cridland@clues.ltd.uk
URI: http://www.clues.ltd.uk/
Alexey Melnikov
ACI WorldWide / MessagingDirect
EMail: mel@messagingdirect.com
URI: http://orthanc.ab.ca/mel/
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