Internet Message Access Protocol (IMAP) Capabilities Registry
Internet Message Access Protocol (IMAP) Capabilities
2026-02-27
IMAP Capabilities
IETF Review
Client implementations compliant with SHOULD NOT require any
capability name other than "IMAP4rev1". Client implementations
compliant with 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 .
ACL
ANNOTATE-EXPERIMENT-1
APPENDLIMIT
AUTH=
BINARY
CATENATE
CHILDREN
COMPRESS=DEFLATE
CONDSTORE
CONTEXT=SEARCH
CONTEXT=SORT
CONVERT
CREATE-SPECIAL-USE
ENABLE
ESEARCH
ESORT
FILTERS
I18NLEVEL=1
I18NLEVEL=2
ID
IDLE
IMAP4REV1
IMAP4REV2
IMAPSIEVE=
INPROGRESS
JMAPACCESS
LANGUAGE
LIST-EXTENDED
LIST-METADATA
LIST-MYRIGHTS
LIST-STATUS
LITERAL+
LITERAL-
LOGIN-REFERRALS
LOGINDISABLED
MAILBOX-REFERRALS
MESSAGELIMIT=
METADATA
METADATA-SERVER
MOVE
MULTIAPPEND
MULTISEARCH
NAMESPACE
NOTIFY
OBJECTID
PARTIAL
PREVIEW
QRESYNC
QUOTA
QUOTA=
QUOTASET
REPLACE
RIGHTS=
SASL-IR
SAVEDATE
SAVELIMIT=
SEARCH=FUZZY
SEARCHRES
SORT
SORT=DISPLAY
SPECIAL-USE
STARTTLS
STATUS=SIZE
THREAD
UIDBATCHES
UIDONLY
UIDPLUS
UNAUTHENTICATE
UNSELECT
URL-PARTIAL
URLAUTH
URLAUTH=BINARY
UTF8=ACCEPT
UTF8=ALL (OBSOLETE)
UTF8=APPEND (OBSOLETE)
UTF8=ONLY
UTF8=USER (OBSOLETE)
WITHIN
IMAP Quota Resource Types
Specification Required
Alexey Melnikov, Ken Murchison
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
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
RFC9208, Section 5.2
MAILBOX
The number of mailboxes governed by the quota root.
N/A
N/A
RFC9208, Section 5.3
ANNOTATION-STORAGE
The maximum size of all annotations , in units of 1024 octets,
associated with all messages in the mailboxes governed by the quota root.
N/A
N/A
RFC9208, Section 5.4
Alexey Melnikov
mailto:alexey.melnikov&isode.com
2021-12-09
IESG
mailto:iesg&ietf.org
2021-12-09