Internet Message Access Protocol (IMAP) Capabilities Registry

Last Updated

  • 2026-08-04

Available Formats

IMAP Capabilities

Registration Procedure(s)

  • IETF Review

Reference

  • RFC 3501: INTERNET MESSAGE ACCESS PROTOCOL - VERSION 4rev1
  • RFC 9051: Internet Message Access Protocol (IMAP) - Version 4rev2

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

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

Available Formats

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

Contact Information

Name Contact URI Last Updated
Alexey Melnikov alexey.melnikov&isode.com 2021-12-09
IESG iesg&ietf.org 2021-12-09