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Keywords: [--------], imap
Network Working Group R. Gellens
Request for Comments: 5423 QUALCOMM Inc.
Category: Standards Track C. Newman
Sun Microsystems
March 2009
Internet Message Store Events
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.
Copyright Notice
Copyright (c) 2009 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents in effect on the date of
publication of this document (http://trustee.ietf.org/license-info).
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document.
Abstract
One of the missing features in the existing Internet mail and
messaging standards is a facility for server-to-server and server-to-
client event notifications related to message store events. As the
scope of Internet mail expands to support more diverse media (such as
voice mail) and devices (such as cell phones) and to provide rich
interactions with other services (such as web portals and legal
compliance systems), the need for an interoperable notification
system increases. This document attempts to enumerate the types of
events that interest real-world consumers of such a system.
This document describes events and event parameters that are useful
for several cases, including notification to administrative systems
and end users. This is not intended as a replacement for a message
access facility such as IMAP.
Gellens & Newman Standards Track [Page 1]
RFC 5423 Internet Message Store Events March 2009
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Conventions Used in This Document . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Event Model . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Event Types . . . . . . . . . . . . . . . . . . . . . . . . . 5
4.1. Message Addition and Deletion . . . . . . . . . . . . . . 5
4.2. Message Flags . . . . . . . . . . . . . . . . . . . . . . 7
4.3. Access Accounting . . . . . . . . . . . . . . . . . . . . 8
4.4. Mailbox Management . . . . . . . . . . . . . . . . . . . . 8
5. Event Parameters . . . . . . . . . . . . . . . . . . . . . . . 10
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
7. Security Considerations . . . . . . . . . . . . . . . . . . . 14
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 15
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 15
9.1. Normative References . . . . . . . . . . . . . . . . . . . 15
9.2. Informative References . . . . . . . . . . . . . . . . . . 15
Appendix A. Future Extensions . . . . . . . . . . . . . . . . . . 17
1. Introduction
A message store is used to organize Internet Messages [RFC5322] into
one or more mailboxes (possibly hierarchical), annotate them in
various ways, and provide access to these messages and associated
metadata. Three different standards-based protocols have been widely
deployed to remotely access a message store. The Post Office
Protocol (POP) [RFC1939] provides simple download-and-delete access
to a single mail drop (which is a subset of the functionality
typically associated with a message store). The Internet Message
Access Protocol (IMAP) [RFC3501] provides an extensible feature-rich
model for online, offline, and disconnected access to a message store
with minimal constraints on any associated "fat-client" user
interface. Finally, mail access applications built on top of the
Hypertext Transfer Protocol (HTTP) [RFC2616] that run in standards-
based web browsers provide a third standards-based access mechanism
for online-only access.
While simple and/or ad-hoc mechanisms for notifications have sufficed
to some degree in the past (e.g., "Simple New Mail Notification"
[RFC4146], "IMAP4 IDLE Command" [RFC2177]), as the scope and
importance of message stores expand, the demand for a more complete
store notification system increases. Some of the driving forces
behind this demand include:
o Mobile devices with intermittent network connectivity that have
"new mail" or "message count" indicators.
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RFC 5423 Internet Message Store Events March 2009
o Unified messaging systems that include both Internet and voice
mail require support for a message-waiting indicator on phones.
o Interaction with systems for event-based or utility-computing
billing.
o Simplification of the process of passing message store events to
non-Internet notification systems.
o A calendar system may wish to subscribe to MessageNew
notifications in order to support iMIP [RFC2447].
o Some jurisdictions have laws or regulations for information
protection and auditing that require interoperable protocols
between message stores built by messaging experts and compliance
auditing systems built by compliance experts.
Vendors who have deployed proprietary notification systems for their
Internet message stores have seen significant demand to provide
notifications for more and more events. As a first step towards
building a notification system, this document attempts to enumerate
the core events that real-world customers demand.
This document includes those events that can be generated by the use
of IMAP4rev1 [RFC3501] and some existing extensions. As new IMAP
extensions are defined, or additional event types or parameters need
to be added, the set specified here can be extended by means of an
IANA registry with update requirements, as specified in Section 6.
1.1. Conventions Used in This Document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
When these words appear in lower-case or with initial capital
letters, they are not RFC 2119 key words.
2. Terminology
The following terminology is used in this document:
mailbox
A container for Internet messages and/or child mailboxes. A
mailbox may or may not permit delivery of new messages via a mail
delivery agent.
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RFC 5423 Internet Message Store Events March 2009
mailbox identifier
A mailbox identifier provides sufficient information to identify a
specific mailbox on a specific server instance. An IMAP URL can
be a mailbox identifier.
message access protocols
Protocols that provide clients (e.g., a mail user agent or web
browser) with access to the message store, including but not
limited to IMAP, POP, and HTTP.
message context
As defined in [RFC3458].
UIDVALIDITY
As defined in IMAP4rev1 [RFC3501]. UIDVALIDITY is critical to the
correct operation of a caching mail client. When it changes, the
client MUST flush its cache. It's particularly important to
include UIDVALIDITY with event notifications related to message
addition or removal in order to keep the message data correctly
synchronized.
3. Event Model
The events that are generated by a message store depend to some
degree on the model used to represent a message store. The model the
IETF has for a message store is implicit from IMAP4rev1 and
extensions, so that model is assumed by this document.
A message store event typically has an associated mailbox name and
usually has an associated user name (or authorization identity if
using the terminology from "Simple Authentication and Security Layer"
(SASL) [RFC4422]). Events referring to a specific message can use an
IMAP URL [RFC5092] to do so. Events referring to a set of messages
can use an IMAP URL to the mailbox plus an IMAP UID (Unique
Identifier) set.
Each notification has a type and parameters. The type determines the
type of event, while the parameters supply information about the
context of the event that may be used to adjust subscription
preferences or may simply supply data associated with the event. The
types and parameter names in this document are restricted to US-ASCII
printable characters, so these events can be easily mapped to an
arbitrary notification system. However, this document assumes that
arbitrary parameter values (including large and multi-line values)
can be encoded with the notification system. Systems which lack that
feature could only implement a subset of these events.
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This document does not indicate which event parameters are mandatory
or optional. That is done in documents that specify specific message
formats or bindings to a notification system.
For scalability reasons, some degree of filtering at event generation
is necessary. At the very least, the ability to turn on and off
groups of related events and to suppress inclusion of large
parameters (such as messageContent) is needed. A sophisticated
publish/subscribe notification system may be able to propagate
cumulative subscription information to the publisher.
Some of these events might be logically collapsed into a single event
type with a required parameter to distinguish between the cases
(e.g., QuotaExceed and QuotaWithin). However, until such time that
an event subscription model is formulated, it's not practical to make
such decisions. We thus note only the fact that some of these events
may be viewed as a single event type.
4. Event Types
This section discusses the different types of events useful in a
message store event notification system. The intention is to
document the events sufficient to cover an overwhelming majority of
known use cases while leaving less common event types for the future.
This section mentions parameters that are important or specific to
the events described here. Event parameters likely to be included in
most or all notifications are discussed in the next section.
4.1. Message Addition and Deletion
This section includes events related to message addition and
deletion.
MessageAppend
A message was appended or concatenated to a mailbox by a message
access client. For the most part, this is identical to the
MessageNew event type except that the SMTP envelope information is
not included as a parameter, but information about which protocol
triggered the event MAY be included. See the MessageNew event for
more information.
MessageExpire
One or more messages were expired from a mailbox due to server
expiration policy and are no longer accessible by the end user.
The parameters include a mailbox identifier that MUST include
UIDVALIDITY and a UID set that describes the messages.
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Information about which server expiration policy was applied may
be included in the future.
MessageExpunge
One or more messages were expunged from a mailbox by an IMAP
CLOSE/EXPUNGE, POP3 DELE+QUIT, HTTP, or equivalent client action
and are no longer accessible by the end user.
The parameters include a mailbox identifier that MUST include
UIDVALIDITY, a UID set, and MAY also indicate which access
protocol triggered the event.
MessageNew
A new message was received into a mailbox via a message delivery
agent.
The parameters include a message identifier that, for IMAP-
accessible message stores, MUST include UIDVALIDITY and a UID.
The parameters MAY also include an SMTP envelope and other
arbitrary message and mailbox metadata. In some cases, the entire
new message itself may be included. The set of parameters SHOULD
be adjustable to the client's preference, with limits set by
server policy. An interesting policy, for example, would be to
include messages up to 2K in size with the notification, but to
include a URLAUTH [RFC4467] reference for larger messages.
QuotaExceed
An operation failed (typically MessageNew) because the user's
mailbox exceeded one of the quotas (e.g., disk quota, message
quota, quota by message context, etc.). The parameters SHOULD
include at least the relevant user and quota and, optionally, the
mailbox. Quota usage SHOULD be included if possible. Parameters
needed to extend this to support quota by context are not
presently described in this document but could be added in the
future.
QuotaWithin
An operation occurred (typically MessageExpunge or MessageExpire)
that reduced the user's quota usage under the limit.
QuotaChange
The user's quota was changed.
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4.2. Message Flags
This section includes events related to changes in message flags.
MessageRead
One or more messages in the mailbox were marked as read or seen by
a user. Note that POP has no concept of read or seen messages, so
these events are only generated by IMAP or HTTP clients (or
equivalent).
The parameters include a mailbox identifier and a set of message
UIDs.
MessageTrash
One or more messages were marked for future deletion by the user
but are still accessible over the protocol (the user's client may
or may not make these messages accessible through its user
interface).
The parameters include a mailbox identifier and a set of message
UIDs.
FlagsSet
One or more messages in the mailbox had one or more IMAP flags or
keywords set.
The parameters include a list of IMAP flag or keyword names that
were set, a mailbox identifier, and the set of UIDs of affected
messages. The flagNames MUST NOT include \Recent. For
compatibility with simpler clients, it SHOULD be configurable
whether setting the \Seen or \Deleted flags results in this event
or the simpler MessageRead/MessageTrash events. By default, the
simpler message forms SHOULD be used for MessageRead and
MessageTrash.
FlagsClear
One or more messages in the mailbox had one or more IMAP flags or
keywords cleared.
The parameters include a list of IMAP flag or keyword names that
were cleared, a mailbox identifier, and the set of UIDs of
affected messages. The flagNames parameter MUST NOT include
\Recent.
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4.3. Access Accounting
This section lists events related to message store access accounting.
Login
A user has logged into the system via IMAP, HTTP, POP, or some
other mechanism.
The parameters include the domain name and port used to access the
server and the user's authorization identity. Additional possible
parameters include the client's IP address and port, the
authentication identity (if different from the authorization
identity), the service name, the authentication mechanism,
information about any negotiated security layers, a timestamp, and
other information.
Logout
A user has logged out or otherwise been disconnected from the
message store via IMAP, HTTP, POP, or some other mechanism.
The parameters include the server domain name and the user's
authorization identity. Additional parameters MAY include any of
the information from the "Login" event as well as information
about the type of disconnect (suggested values include graceful,
abort, timeout, and security layer error), the duration of the
connection or session, and other information.
4.4. Mailbox Management
This section lists events related to the management of mailboxes.
MailboxCreate
A mailbox has been created, or an access control changed on an
existing mailbox so that it is now accessible by the user. If the
mailbox creation caused the creation of new mailboxes earlier in
the hierarchy, separate MailboxCreate events are not generated, as
their creation is implied.
The parameters include the created mailbox identifier, its
UIDVALIDITY for IMAP-accessible message stores, and MAY also
indicate which access protocol triggered the event. Access and
permissions information (such as Access Control List (ACL)
[RFC4314] settings) require a standardized format to be included,
and so are left for future extension.
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MailboxDelete
A mailbox has been deleted, or an access control changed on an
existing mailbox so that it is no longer accessible by the user.
Note that if the mailbox has child mailboxes, only the specified
mailbox has been deleted, not the children. The mailbox becomes
\NOSELECT, and the hierarchy remains unchanged, as per the
description of the DELETE command in IMAP4rev1 [RFC3501].
The parameters include the deleted mailbox identifier and MAY also
indicate which access protocol triggered the event.
MailboxRename
A mailbox has been renamed. Note that, per the description of the
RENAME command in IMAP4rev1 [RFC3501], special semantics regarding
the mailbox hierarchy apply when INBOX is renamed (child mailboxes
are usually included in the rename, but are excluded when INBOX is
renamed). When a mailbox other than INBOX is renamed and its
child mailboxes are also renamed as a result, separate
MailboxRename events are not generated for the child mailboxes, as
their renaming is implied. If the rename caused the creation of
new mailboxes earlier in the hierarchy, separate MailboxCreate
events are not generated for those, as their creation is implied.
When INBOX is renamed, a new INBOX is created. A MailboxCreate
event is not generated for the new INBOX, since it is implied.
The parameters include the old mailbox identifier, the new mailbox
identifier, and MAY also indicate which access protocol triggered
the event.
MailboxSubscribe
A mailbox has been added to the server-stored subscription list,
such as the one managed by the IMAP SUBSCRIBE and UNSUBSCRIBE
commands.
The parameters include the user whose subscription list has been
affected, the mailbox identifier, and MAY also indicate which
access protocol triggered the event.
MailboxUnSubscribe
A mailbox has been removed from the subscription list.
The parameters include the user whose subscription list has been
affected, the mailbox identifier, and MAY also indicate which
access protocol triggered the event.
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5. Event Parameters
This section lists parameters included with these events.
admin
Included with all events generated by message access protocols.
The authentication identity associated with this event, as
distinct from the authorization identity (see "user"). This is
not included when it is the same as the value of the user
parameter.
bodyStructure
May be included with MessageAppend and MessageNew.
The IMAP BODYSTRUCTURE of the message.
clientIP
Included with all events generated by message access protocols.
The IPv4 or IPv6 address of the message store access client that
performed the action that triggered the notification.
clientPort
Included with all events generated by message access protocols.
The port number of the message store access client that performed
an action that triggered the notification (the port from which the
connection occurred).
diskQuota
Included with QuotaExceed, QuotaWithin, and QuotaChange
notifications relating to a user or mailbox disk quota. May be
included with other notifications.
Disk quota limit in kilobytes (1024 octets).
diskUsed
Included with QuotaExceed and QuotaWithin notifications relating
to a user or mailbox disk quota. May be included with other
notifications.
Disk space used in kilobytes (1024 octets). Only disk space that
counts against the quota is included.
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envelope
May be included with the MessageNew notification.
The message transfer envelope associated with final delivery of
the message for the MessageNew notification. This includes the
MAIL FROM and relevant RCPT TO line(s) used for final delivery
with CRLF delimiters and any ESMTP parameters.
flagNames
Included with FlagsSet and FlagsClear events. May be included
with MessageAppend and MessageNew to indicate flags that were set
initially by the APPEND command or delivery agent, respectively.
A list (likely to be space-separated) of IMAP flag or keyword
names that were set or cleared. Flag names begin with a backslash
while keyword names do not. The \Recent flag is explicitly not
permitted in the list.
mailboxID
Included in events that affect mailboxes. A URI describing the
mailbox. In the case of MailboxRename, this refers to the new
name.
maxMessages
Included with QuotaExceed and QuotaWithin notifications relating
to a user or mailbox message count quota. May be included with
other notifications.
Quota limit on the number of messages in the mailbox, for events
referring to a mailbox.
messageContent
May be included with MessageAppend and MessageNew.
The entire message itself. Size-based suppression of this SHOULD
be available.
messageSize
May be included with MessageAppend and MessageNew.
Size of the RFC 5322 message itself in octets. This value matches
the length of the IMAP literal returned in response to an IMAP
FETCH of BODY[] for the referenced message.
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messages
Included with QuotaExceed and QuotaWithin notifications relating
to a user or mailbox message count quota. May be included with
other notifications.
Number of messages in the mailbox. This is typically included
with message addition and deletion events.
modseq
May be included with any notification referring to one message.
This is the 64-bit integer MODSEQ as defined in [RFC4551]. No
assumptions about MODSEQ can be made if this is omitted.
oldMailboxID
A URI describing the old name of a renamed or moved mailbox.
pid
May be included with any notification.
The process ID of the process that generated the notification.
process
May be included with any notification.
The name of the process that generated the notification.
serverDomain
Included in Login and optionally in Logout or other events. The
domain name or IP address (v4 or v6) used to access the server or
mailbox.
serverPort
Included in Login and optionally in Logout or other events. The
port number used to access the server. This is often a well-known
port.
serverFQDN
May be included with any notification.
The fully qualified domain name of the server that generated the
event. Note that this may be different from the server name used
to access the mailbox included in the mailbox identifier.
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service
May be included with any notification.
The name of the service that triggered the event. Suggested
values include "imap", "pop", "http", and "admincli" (for an
administrative client).
tags
May be included with any notification.
A list of UTF-8 tags (likely to be comma-separated). One or more
tags can be set at the time a notification criteria or
notification subscription is created. Subscribers can use tags
for additional client-side filtering or dispatch of events.
timestamp
May be included with any notification.
The time at which the event occurred that triggered the
notification (the underlying protocol carrying the notification
may contain a timestamp for when the notification was generated).
This MAY be an approximate time.
Timestamps are expressed in local time and contain the offset from
UTC (this information is used in several places in Internet mail)
and are normally in [RFC3339] format.
uidnext
May be included with any notification referring to a mailbox.
The UID that is projected to be assigned next in the mailbox.
This is typically included with message addition and deletion
events. This is equivalent to the UIDNEXT status item in the IMAP
STATUS command.
uidset
Included with MessageExpires, MessageExpunges, MessageRead,
MessageTrash, FlagsSet, and FlagsClear.
This includes the set of IMAP UIDs referenced.
uri
Included with all notifications. A reference to the IMAP server,
a mailbox, or a message.
Typically an IMAP URL. This can include the name of the server
used to access the mailbox/message, the mailbox name, the
UIDVALIDITY of the mailbox, and the UID of a specific message.
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user
Included with all events generated by message access protocols.
This is the authorization identifier used when the client
connected to the access protocol that triggered the event. Some
protocols (for example, many SASL mechanisms) distinguish between
authorization and authentication identifiers. For events
associated with a mailbox, this may be different from the owner of
the mailbox specified in the IMAP URL.
6. IANA Considerations
The IANA has created a new registry for "Internet Message Store
Events" that contains two sub-registries: event names and event
parameters. For both event names and event parameters, entries that
do not start with "vnd." are added by the IETF and are intended for
interoperable use. Entries that start with "vnd." are intended for
private use by one or more parties and are allocated to avoid
collisions.
The initial values are contained in this document.
Using IANA Considerations [RFC5226] terminology, entries that do not
start with "vnd." are allocated by IETF Consensus, while those
starting with "vnd." are allocated First Come First Served.
7. Security Considerations
Notifications can produce a large amount of traffic and expose
sensitive information. When notification mechanisms are used to
maintain state between different entities, the ability to corrupt or
manipulate notification messages could enable an attacker to modulate
the state of these entities. For example, if an attacker were able
to modify notifications sent from a message store to an auditing
server, he could modify the "user" and "messageContent" parameters in
MessageNew notifications to create false audit log entries.
A competent transfer protocol for notifications must consider
authentication, authorization, privacy, and message integrity, as
well as denial-of-service issues. While the IETF has adequate tools
and experience to address these issues for mechanisms that involve
only one TCP connection, notification or publish/subscribe protocols
that are more sophisticated than a single end-to-end TCP connection
will need to pay extra attention to these issues and carefully
balance requirements to successfully deploy a system with security
and privacy considerations.
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8. Acknowledgments
Alexey Melnikov, Arnt Gulbrandsen, and Zoltan Ordogh have reviewed
and offered improvements to this document. Richard Barnes did a nice
review during Last Call.
9. References
9.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3501] Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION
4rev1", RFC 3501, March 2003.
[RFC5092] Melnikov, A. and C. Newman, "IMAP URL Scheme", RFC 5092,
November 2007.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
May 2008.
9.2. Informative References
[RFC1939] Myers, J. and M. Rose, "Post Office Protocol - Version 3",
STD 53, RFC 1939, May 1996.
[RFC2177] Leiba, B., "IMAP4 IDLE command", RFC 2177, June 1997.
[RFC2447] Dawson, F., Mansour, S., and S. Silverberg, "iCalendar
Message-Based Interoperability Protocol (iMIP)", RFC 2447,
November 1998.
[RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.
[RFC3339] Klyne, G., Ed. and C. Newman, "Date and Time on the
Internet: Timestamps", RFC 3339, July 2002.
[RFC3458] Burger, E., Candell, E., Eliot, C., and G. Klyne, "Message
Context for Internet Mail", RFC 3458, January 2003.
[RFC4146] Gellens, R., "Simple New Mail Notification", RFC 4146,
August 2005.
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[RFC4314] Melnikov, A., "IMAP4 Access Control List (ACL) Extension",
RFC 4314, December 2005.
[RFC4422] Melnikov, A. and K. Zeilenga, "Simple Authentication and
Security Layer (SASL)", RFC 4422, June 2006.
[RFC4467] Crispin, M., "Internet Message Access Protocol (IMAP) -
URLAUTH Extension", RFC 4467, May 2006.
[RFC4551] Melnikov, A. and S. Hole, "IMAP Extension for Conditional
STORE Operation or Quick Flag Changes Resynchronization",
RFC 4551, June 2006.
[RFC5322] Resnick, P., Ed., "Internet Message Format", RFC 5322,
October 2008.
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Appendix A. Future Extensions
This document specifies core functionality based on events that are
believed to be well understood, have known use cases, and are
implemented by at least one deployed real-world Internet message
store. (A few events are exceptions to the last test only: FlagsSet,
FlagsClear, MailboxCreate, MailboxDelete, MailboxRename,
MailboxSubscribe, and MailboxUnSubscribe.)
Some events have been suggested but are postponed to future
extensions because they do not meet this criteria. These events
include messages that have been moved to archive storage and may
require extra time to access, quota by message context,
authentication failure, user mail account disabled, annotations, and
mailbox ACL or metadata change. The descriptions of several events
note additional parameters that are likely candidates for future
inclusion. See Section 6 for how the list of events and parameters
can be extended.
In order to narrow the scope of this document to something that can
be completed, only events generated from the message store (by a
message access module, administrative module, or message delivery
agent) are considered. A complete mail system is normally linked
with an identity system that would also publish events of interest to
a message store event subscriber. Events of interest include account
created/deleted/disabled and password changed/expired.
Authors' Addresses
Randall Gellens
QUALCOMM Incorporated
5775 Morehouse Drive
San Diego, CA 92651
USA
Phone:
EMail: rg+ietf@qualcomm.com
Chris Newman
Sun Microsystems
800 Royal Oaks
Monrovia, CA 91016-6347
USA
Phone:
EMail: chris.newman@sun.com
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