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                                            Internet Message Access Protocol (IMAP) Capabilities Registry

Last Updated
        2026-08-04

Available Formats
        [IMG]
        XML [IMG]
        HTML [IMG]
        TXT

Registries Included Below

  • IMAP Capabilities
  • IMAP Quota Resource Types

IMAP Capabilities

Registration Procedure(s)

             IETF Review


Reference
        [RFC 3501][RFC 9051]

Note

 Client implementations compliant with [RFC 3501] SHOULD NOT require any
 capability name other than "IMAP4rev1". Client implementations
 compliant with [RFC 9051] SHOULD NOT require any capability name other
 than "IMAP4rev2", and possibly "STARTTLS" and "LOGINDISABLED" (on a
 cleartext port). All client implementations MUST ignore any unknown
 capability names.

 The prefix "QUOTA=RES-" is reserved per [RFC 9208, Section 9.1].
 See [Section 9.2 of RFC 9208] for values that follow this prefix.

 All other capabilities starting with the "QUOTA=" prefix are reserved
 for future IETF Stream extensions to [RFC 9208].

Available Formats
        [IMG]
        CSV

   Capability Name               Reference
ACL                    [RFC 4314]
ANNOTATE-EXPERIMENT-1  [RFC 5257]
APPENDLIMIT            [RFC 7889]
AUTH=                  [RFC 3501]; [RFC 9051]
BINARY                 [RFC 3516]
CATENATE               [RFC 4469]
CHILDREN               [RFC 3348]
COMPRESS=DEFLATE       [RFC 4978]
CONDSTORE              [RFC 7162]
CONTEXT=SEARCH         [RFC 5267]
CONTEXT=SORT           [RFC 5267]
CONVERT                [RFC 5259]
CREATE-SPECIAL-USE     [RFC 6154]
ENABLE                 [RFC 5161]
ESEARCH                [RFC 4731]
ESORT                  [RFC 5267]
FILTERS                [RFC 5466]
I18NLEVEL=1            [RFC 5255]
I18NLEVEL=2            [RFC 5255]
ID                     [RFC 2971]
IDLE                   [RFC 2177]
IMAP4REV1              [RFC 3501]
IMAP4REV2              [RFC 9051]
IMAPSIEVE=             [RFC 6785]
INPROGRESS             [RFC 9585]
JMAPACCESS             [RFC 9698]
LANGUAGE               [RFC 5255]
LIST-EXTENDED          [RFC 5258]
LIST-METADATA          [RFC 9590]
LIST-MYRIGHTS          [RFC 8440]
LIST-STATUS            [RFC 5819]
LITERAL+               [RFC 7888]
LITERAL-               [RFC 7888]
LOGIN-REFERRALS        [RFC 2221]
LOGINDISABLED          [RFC 3501]; [RFC 9051]
MAILBOX-REFERRALS      [RFC 2193]
MESSAGELIMIT=          [RFC 9738]
METADATA               [RFC 5464]
METADATA-SERVER        [RFC 5464]
MOVE                   [RFC 6851]
MULTIAPPEND            [RFC 3502]
MULTISEARCH            [RFC 7377]
NAMESPACE              [RFC 2342]
NOTIFY                 [RFC 5465]
OBJECTID               [RFC 8474]
PARTIAL                [RFC 9394]
PREVIEW                [RFC 8970]
QRESYNC                [RFC 7162]
QUOTA                  [RFC 9208]
QUOTA=                 [RFC 9208]
QUOTASET               [RFC 9208]
REPLACE                [RFC 8508]
RIGHTS=                [RFC 4314]
SASL-IR                [RFC 4959]
SAVEDATE               [RFC 8514]
SAVELIMIT=             [RFC 9738]
SEARCH=FUZZY           [RFC 6203]
SEARCHRES              [RFC 5182]
SORT                   [RFC 5256]
SORT=DISPLAY           [RFC 5957]
SPECIAL-USE            [RFC 6154]
STARTTLS               [RFC 3501]; [RFC 9051]
STATUS=SIZE            [RFC 8438]
THREAD                 [RFC 5256]
UIDBATCHES             [RFC 10022]
UIDONLY                [RFC 9586]
UIDPLUS                [RFC 4315]
UNAUTHENTICATE         [RFC 8437]
UNSELECT               [RFC 3691]
URL-PARTIAL            [RFC 5550]
URLAUTH                [RFC 4467]
URLAUTH=BINARY         [RFC 5524]; [RFC Errata 6214]
UTF8=ACCEPT            [RFC 9755]
UTF8=ALL (OBSOLETE)    [RFC 5738]; [RFC 9755]
UTF8=APPEND (OBSOLETE) [RFC 5738]; [RFC 9755]
UTF8=ONLY              [RFC 9755]
UTF8=USER (OBSOLETE)   [RFC 5738]; [RFC 9755]
WITHIN                 [RFC 5032]

IMAP Quota Resource Types

Registration Procedure(s)

             Specification Required


Expert(s)

             Alexey Melnikov, Ken Murchison


Reference
        [RFC 9208]

Available Formats
        [IMG]
        CSV

Name of the Quota                   Description                    Extra required IMAP   Extra optional IMAP      Author         Change    Reference
  Resource Type                                                     commands/responses   commands/responses                    Controller
                   The physical space estimate, in units of 1024  DELETED-STORAGE STATUS                                                  [RFC 9208,
STORAGE            octets, of the mailboxes governed by the quota request data item and  N/A                 [Alexey_Melnikov] [IESG]     Section 5.1]
                   root.                                          response data item
                   The number of messages stored within the       DELETED STATUS request                                                  [RFC 9208,
MESSAGE            mailboxes governed by the quota root.          data item and response N/A                 [Alexey_Melnikov] [IESG]     Section 5.2]
                                                                  data item
MAILBOX            The number of mailboxes governed by the quota  N/A                    N/A                 [Alexey_Melnikov] [IESG]     [RFC 9208,
                   root.                                                                                                                  Section 5.3]
                   The maximum size of all annotations [RFC
ANNOTATION-STORAGE 5257], in units of 1024 octets, associated     N/A                    N/A                 [Alexey_Melnikov] [IESG]     [RFC 9208,
                   with all messages in the mailboxes governed by                                                                         Section 5.4]
                   the quota root.

                                                                 Contact Information

       ID              Name                 Contact URI            Last Updated
[Alexey_Melnikov] Alexey Melnikov mailto:alexey.melnikov&isode.com 2021-12-09
[IESG]            IESG            mailto:iesg&ietf.org             2021-12-09

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