IMAP4 QUOTA extension

Status of this Memo

This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "Internet Official Protocol Standards" (STD 1) for the standardization state and status of this protocol. Distribution of this memo is unlimited.

1. Abstract

The QUOTA extension of the Internet Message Access Protocol [IMAP4] permits administrative limits on resource usage (quotas) to be manipulated through the IMAP protocol.

Table of Contents

   1.   Abstract........................................... 1
   2.   Conventions Used in this Document.................. 1
   3.   Introduction and Overview.......................... 2
   4.   Commands........................................... 2
   4.1. SETQUOTA Command................................... 2
   4.2. GETQUOTA Command................................... 2
   4.3. GETQUOTAROOT Command............................... 3
   5.   Responses.......................................... 3
   5.1. QUOTA Response..................................... 3
   5.2. QUOTAROOT Response................................. 4
   6.   Formal syntax...................................... 4
   7.   References......................................... 5
   8.   Security Considerations............................ 5
   9.   Author's Address................................... 5

2. Conventions Used in this Document

In examples, "C:" and "S:" indicate lines sent by the client and server respectively.

3. Introduction and Overview

The QUOTA extension is present in any IMAP4 implementation which returns "QUOTA" as one of the supported capabilities to the CAPABILITY command.

An IMAP4 server which supports the QUOTA capability may support limits on any number of resources. Each resource has an atom name and an implementation-defined interpretation which evaluates to an integer. Examples of such resources are:

      Name       Interpretation
      
      STORAGE    Sum of messages' RFC822.SIZE, in units of 1024 octets
      MESSAGE    Number of messages

Each mailbox has zero or more implementation-defined named "quota roots". Each quota root has zero or more resource limits. All mailboxes that share the same named quota root share the resource limits of the quota root.

Quota root names do not necessarily have to match the names of existing mailboxes.

4. Commands

4.1. SETQUOTA Command

   Arguments:  quota root
               list of resource limits
   
   Data:       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.

   Example:    C: A001 SETQUOTA "" (STORAGE 512)
               S: * QUOTA "" (STORAGE 10 512)
               S: A001 OK Setquota completed

4.2. GETQUOTA Command

   Arguments:  quota root
   
   Data:       untagged responses: QUOTA
   
   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.

   Example:    C: A003 GETQUOTA ""
               S: * QUOTA "" (STORAGE 10 512)
               S: A003 OK Getquota completed

4.3. GETQUOTAROOT Command

   Arguments:  mailbox name
   
   Data:       untagged responses: QUOTAROOT, QUOTA
   
   Result:     OK - getquota completed
               NO - getquota error: no such mailbox, permission denied
               BAD - command unknown or arguments invalid

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.

   Example:    C: A003 GETQUOTAROOT INBOX
               S: * QUOTAROOT INBOX ""
               S: * QUOTA "" (STORAGE 10 512)
               S: A003 OK Getquota completed

5. Responses

5.1. QUOTA Response

   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 triplets. Each triplet conatins 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)

5.2. QUOTAROOT Response

   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

6. Formal syntax

The following syntax specification uses the augmented Backus-Naur Form (BNF) notation as specified in RFC 822 with one exception; the delimiter used with the "#" construct is a single space (SP) and not one or more commas.

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 astring
   
   getquotaroot    ::= "GETQUOTAROOT" SP astring
   
   quota_list      ::= "(" #quota_resource ")"
   
   quota_resource  ::= atom SP number SP number
   
   quota_response  ::= "QUOTA" SP astring SP quota_list

quotaroot_response

                   ::= "QUOTAROOT" SP astring *(SP astring)
   
   setquota        ::= "SETQUOTA" SP astring SP setquota_list
   
   setquota_list   ::= "(" 0#setquota_resource ")"
   
   setquota_resource ::= atom SP number

7. References

   [IMAP4] Crispin, M., "Internet Message Access Protocol - Version 4",
   RFC 1730, University of Washington, December 1994.
   
   [RFC-822] Crocker, D., "Standard for    the Format of ARPA Internet
   Text Messages", STD 11, RFC 822.

8. Security Considerations

Implementors should be careful to make sure the implementation of these commands does not violate the site's security policy. The resource usage of other users is likely to be considered confidential information and should not be divulged to unauthorized persons.

9. Author's Address

   John G. Myers
   Carnegie-Mellon University
   5000 Forbes Ave.
   Pittsburgh PA, 15213-3890
   
   EMail: jgm+@cmu.edu