Internet Message Access Protocol (IMAP) Capabilities Registry

Last Updated
2025-03-18
Available Formats

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Registries Included Below

IMAP Capabilities

Registration Procedure(s)
IETF Review
Reference
[RFC3501][RFC9051]
Note
Client implementations compliant with [RFC3501] SHOULD NOT require any 
capability name other than "IMAP4rev1". Client implementations 
compliant with [RFC9051] 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 [RFC9208, Section 9.1].
See Section 9.2 of that document for values that follow this prefix.

All other capabilities starting with the "QUOTA=" prefix are reserved 
for future IETF Stream extensions to [RFC9208].
Available Formats

CSV
Capability Name Reference
ACL [RFC4314]
ANNOTATE-EXPERIMENT-1 [RFC5257]
APPENDLIMIT [RFC7889]
AUTH= [RFC3501][RFC9051]
BINARY [RFC3516]
CATENATE [RFC4469]
CHILDREN [RFC3348]
COMPRESS=DEFLATE [RFC4978]
CONDSTORE [RFC7162]
CONTEXT=SEARCH [RFC5267]
CONTEXT=SORT [RFC5267]
CONVERT [RFC5259]
CREATE-SPECIAL-USE [RFC6154]
ENABLE [RFC5161]
ESEARCH [RFC4731]
ESORT [RFC5267]
FILTERS [RFC5466]
I18NLEVEL=1 [RFC5255]
I18NLEVEL=2 [RFC5255]
ID [RFC2971]
IDLE [RFC2177]
IMAP4REV1 [RFC3501]
IMAP4REV2 [RFC9051]
IMAPSIEVE= [RFC6785]
INPROGRESS [RFC9585]
JMAPACCESS [RFC9698]
LANGUAGE [RFC5255]
LIST-EXTENDED [RFC5258]
LIST-METADATA [RFC9590]
LIST-MYRIGHTS [RFC8440]
LIST-STATUS [RFC5819]
LITERAL+ [RFC7888]
LITERAL- [RFC7888]
LOGIN-REFERRALS [RFC2221]
LOGINDISABLED [RFC3501][RFC9051]
MAILBOX-REFERRALS [RFC2193]
MESSAGELIMIT= [RFC9738]
METADATA [RFC5464]
METADATA-SERVER [RFC5464]
MOVE [RFC6851]
MULTIAPPEND [RFC3502]
MULTISEARCH [RFC7377]
NAMESPACE [RFC2342]
NOTIFY [RFC5465]
OBJECTID [RFC8474]
PARTIAL [RFC9394]
PREVIEW [RFC8970]
QRESYNC [RFC7162]
QUOTA [RFC9208]
QUOTA= [RFC9208]
QUOTASET [RFC9208]
REPLACE [RFC8508]
RIGHTS= [RFC4314]
SASL-IR [RFC4959]
SAVEDATE [RFC8514]
SAVELIMIT= [RFC9738]
SEARCH=FUZZY [RFC6203]
SEARCHRES [RFC5182]
SORT [RFC5256]
SORT=DISPLAY [RFC5957]
SPECIAL-USE [RFC6154]
STARTTLS [RFC3501][RFC9051]
STATUS=SIZE [RFC8438]
THREAD [RFC5256]
UIDONLY [RFC9586]
UIDPLUS [RFC4315]
UNAUTHENTICATE [RFC8437]
UNSELECT [RFC3691]
URL-PARTIAL [RFC5550]
URLAUTH [RFC4467]
URLAUTH=BINARY [RFC5524][RFC Errata 6214]
UTF8=ACCEPT [RFC9755]
UTF8=ALL (OBSOLETE) [RFC5738][RFC9755]
UTF8=APPEND (OBSOLETE) [RFC5738][RFC9755]
UTF8=ONLY [RFC9755]
UTF8=USER (OBSOLETE) [RFC5738][RFC9755]
WITHIN [RFC5032]

IMAP Quota Resource Types

Registration Procedure(s)
Specification Required
Expert(s)
Alexey Melnikov, Ken Murchison
Reference
[RFC9208]
Available Formats

CSV
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] [RFC9208, 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] [RFC9208, Section 5.2]
MAILBOX The number of mailboxes governed by the quota root. N/A N/A [Alexey_Melnikov] [IESG] [RFC9208, Section 5.3]
ANNOTATION-STORAGE The maximum size of all annotations [RFC5257], in units of 1024 octets, associated with all messages in the mailboxes governed by the quota root. N/A N/A [Alexey_Melnikov] [IESG] [RFC9208, Section 5.4]

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