Network Working Group G. Vaudreuil
Request for Comments: 2421 Lucent Technologies
Obsoletes: 1911 G. Parsons
Category: Standards Track Northern Telecom
September 1998
Voice Profile for Internet Mail - version 2
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) The Internet Society (1998). All Rights Reserved.
Overview
This document profiles Internet mail for voice messaging. It
obsoletes RFC 1911 which describes version 1 of the profile. A list
of changes from that document are noted in Appendix F. As well,
Appendix A summarizes the protocol profiles of this version of VPIM.
Please send comments on this document to the EMA VPIM Work Group
mailing list: <vpim-l@ema.org>
Working Group Summary
This profile is not the product of an IETF working group, though
several have reviewed the document. It is instead the product of the
VPIM Work Group of the Electronic Messaging Association (EMA). This
work group, which has representatives from most major voice mail
vendors and several email vendors, has held several interoperability
demonstrations between voice messaging vendors and is currently
promoting VPIM trials and deployment.
Vaudreuil & Parsons Standards Track [Page 1]
RFC 2421 VPIM v2 September 1998
Table of Contents
1. ABSTRACT .........................................................32. SCOPE ............................................................32.1 Voice Messaging System Limitations ............................32.2 Design Goals ..................................................43. PROTOCOL RESTRICTIONS ............................................54. VOICE MESSAGE INTERCHANGE FORMAT .................................64.1 Message Addressing Formats ....................................64.2 Message Header Fields .........................................94.3 Voice Message Content Types ..................................154.4 Other Message Content Types ..................................214.5 Forwarded Messages ...........................................234.6 Reply Messages ...............................................234.7 Notification Messages ........................................245. MESSAGE TRANSPORT PROTOCOL ......................................245.1 ESMTP Commands ...............................................255.2 ESMTP Keywords ...............................................275.3 ESMTP Parameters - MAIL FROM .................................285.4 ESMTP Parameters - RCPT TO ...................................295.5 ESMTP - SMTP Downgrading .....................................296. DIRECTORY ADDRESS RESOLUTION ....................................307. IMAP ............................................................308. MANAGEMENT PROTOCOLS ............................................308.1 Network Management ...........................................319. CONFORMANCE REQUIREMENTS ........................................3110. SECURITY CONSIDERATIONS ........................................3210.1 General Directive ...........................................3210.2 Threats and Problems ........................................3210.3 Security Techniques .........................................3311. REFERENCES .....................................................3312. ACKNOWLEDGMENTS ................................................3613. AUTHORS' ADDRESSES .............................................3614. APPENDIX A - VPIM REQUIREMENTS SUMMARY .........................3715. APPENDIX B - EXAMPLE VOICE MESSAGES ............................4516. APPENDIX C - EXAMPLE ERROR VOICE PROCESSING ERROR CODES ........5017. APPENDIX D - EXAMPLE VOICE PROCESSING DISPOSITION TYPES ........5118. APPENDIX E - IANA REGISTRATIONS ................................5218.1 vCard EMAIL Type Definition for VPIM ........................5218.2 Voice Content-Disposition Parameter Definition ..............5219. APPENDIX F - CHANGE HISTORY: RFC 1911 TO THIS DOCUMENT .........5420. FULL COPYRIGHT NOTICE ..........................................56
Vaudreuil & Parsons Standards Track [Page 2]
RFC 2421 VPIM v2 September 1998
A class of special-purpose computers has evolved to provide voice
messaging services. These machines generally interface to a
telephone switch and provide call answering and voice messaging
services. Traditionally, messages sent to a non-local machine are
transported using analog networking protocols based on DTMF signaling
and analog voice playback. As the demand for networking increases,
there is a need for a standard high-quality digital protocol to
connect these machines. The following document is a profile of the
Internet standard MIME and ESMTP protocols for use as a digital voice
messaging networking protocol. The profile is referred to as VPIM
(Voice Profile for Internet Mail) in this document.
This profile is based on earlier work in the Audio Message
Interchange Specification (AMIS) group that defined a voice messaging
protocol based on X.400 technology. This profile is intended to
satisfy the user requirements statement from that earlier work with
the industry standard ESMTP/MIME mail protocol infrastructures
already used within corporate intranets. This second version of VPIM
is based on implementation experience and obsoletes RFC 1911 which
describes version 1 of the profile.
MIME is the Internet multipurpose, multimedia messaging standard.
This document explicitly recognizes its capabilities and provides a
mechanism for the exchange of various messaging technologies,
primarily voice and facsimile.
This document specifies a restricted profile of the Internet
multimedia messaging protocols for use between voice processing
server platforms. These platforms have historically been special-
purpose computers and often do not have the same facilities normally
associated with a traditional Internet Email-capable computer. As a
result, VPIM also specifies additional functionality as it is needed.
This profile is intended to specify the minimum common set of
features to allow interworking between compliant systems.
The following are typical limitations of voice messaging platform
which were considered in creating this baseline profile.
1) Text messages are not normally received and often cannot be
easily displayed or viewed. They can often be processed only via
text-to-speech or text-to-fax features not currently present in
many of these machines.
Vaudreuil & Parsons Standards Track [Page 3]
RFC 2421 VPIM v2 September 1998
2) Voice mail machines usually act as an integrated Message
Transfer Agent, Message Store and User Agent. There is no relaying
of messages, and RFC 822 header fields may have limited use in the
context of the limited messaging features currently deployed.
3) Voice mail message stores are generally not capable of
preserving the full semantics of an Internet message. As such, use
of a voice mail machine for gatewaying is not supported. In
particular, storage of recipient lists, "Received" lines, and
"Message-ID" may be limited.
4) Internet-style distribution/exploder mailing lists are not
typically supported. Voice mail machines often implement only
local alias lists, with error-to-sender and reply-to-sender
behavior. Reply-all capabilities using a CC list are not generally
available.
5) Error reports must be machine-parsable so that helpful responses
can be voiced to users whose only access mechanism is a telephone.
6) The voice mail systems generally limit address entry to 16 or
fewer numeric characters, and normally do not support alphanumeric
mailbox names. Alpha characters are not generally used for mailbox
identification as they cannot be easily entered from a telephone
terminal.
It is a goal of this profile to make as few restrictions and
additions to the existing Internet mail protocols as possible while
satisfying the requirements for interoperability with current
generation voice messaging systems. This goal is motivated by the
desire to increase the accessibility to digital messaging by enabling
the use of proven existing networking software for rapid development.
This specification is intended for use on a TCP/IP network; however,
it is possible to use the SMTP protocol suite over other transport
protocols. The necessary protocol parameters for such use is outside
the scope of this document.
This profile is intended to be robust enough to be used in an
environment, such as the global Internet with installed-base gateways
which do not understand MIME, though typical use is expected to be
within corporate intranets. Full functionality, such as reliable
error messages and binary transport, will require careful selection
of gateways (e.g., via MX records) to be used as VPIM forwarding
agents. Nothing in this document precludes use of general purpose
MIME email packages to read and compose VPIM messages. While no
Vaudreuil & Parsons Standards Track [Page 4]
RFC 2421 VPIM v2 September 1998
special configuration is required to receive VPIM compliant messages,
some may be required to originate compliant structures.
It is expected that a VPIM messaging system will be managed by a
system administrator who can perform TCP/IP network configuration.
When using facsimile or multiple voice encodings, it is suggested
that the system administrator maintain a list of the capabilities of
the networked mail machines to reduce the sending of undeliverable
messages due to lack of feature support. Configuration,
implementation and management of these directory listing capabilities
are local matters.
This protocol does not limit the number of recipients per message.
Where possible, server implementations should not restrict the number
of recipients in a single message. It is recognized that no
implementation supports unlimited recipients, and that the number of
supported recipients may be quite low.
This protocol does not limit the maximum message length.
Implementers should understand that some machines will be unable to
accept excessively long messages. A mechanism is defined in the RFC
1425 SMTP service extensions to declare the maximum message size
supported.
The message size indicated in the ESMTP SIZE parameter is in bytes,
not minutes or seconds. The number of bytes varies by voice encoding
format and includes the MIME wrapper overhead. If the length must be
known before sending, an approximate translation into minutes or
seconds can be performed if the voice encoding is known.
The following sections describe the restrictions and additions to
Internet mail protocols that are required to be compliant with this
VPIM v2 profile. Though various SMTP, ESMTP and MIME features are
described here, the implementer is referred to the relevant RFCs for
complete details. It is also advisable to check for IETF drafts of
various Internet Mail specifications that are later than the most
recent RFCs since, for example, MIME has yet to be published as a
full IETF Standard. The table in Appendix A summarizes the protocol
details of this profile.
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 [REQ].
Vaudreuil & Parsons Standards Track [Page 5]
RFC 2421 VPIM v2 September 1998
The voice message interchange format is a profile of the Internet
Mail Protocol Suite. Any Internet Mail message containing the format
defined in this section is referred to as a VPIM Message in this
document. As a result, this document assumes an understanding of the
Internet Mail specifications. Specifically, VPIM references
components from the message format standard for Internet messages
[RFC822], the Multipurpose Internet Message Extensions [MIME], the
X.400 gateway specification [X.400], delivery status and message
disposition notifications [REPORT][DSN][DRPT][STATUS][MDN], and the
electronic business card [MIMEDIR][VCARD].
RFC 822 addresses are based on the domain name system. This naming
system has two components: the local part, used for username or
mailbox identification; and the host part, used for global machine
identification.
The local part of the address shall be a US-ASCII string uniquely
identifying a mailbox on a destination system. For voice messaging,
the local part is a printable string containing the mailbox ID of the
originator or recipient. While alpha characters and long mailbox
identifiers are permitted, most voice mail networks rely on numeric
mailbox identifiers to retain compatibility with the limited 10 digit
telephone keypad. As a result, some voice messaging systems may only
be able to handle a numeric local part. The reception of
alphanumeric local parts on these systems may result in the address
being mapped to some locally unique (but confusing to the recipient)
number or, in the worst case the address could be deleted making the
message un-replyable. Additionally, it may be difficult to create
messages on these systems with an alphanumeric local part without
complex key sequences or some form of directory lookup (see 6).
The use of the domain naming system should be transparent to the
user. It is the responsibility of the voice mail machine to lookup
the fully-qualified domain name (FQDN) based on the address entered
by the user (see 6).
In the absence of a global directory, specification of the local part
is expected to conform to international or private telephone
numbering plans. It is likely that private numbering plans will
prevail and these are left for local definition. However, it is
RECOMMENDED that public telephone numbers be noted according to the
international numbering plan described in [E.164]. The indication
Vaudreuil & Parsons Standards Track [Page 6]
RFC 2421 VPIM v2 September 1998
that the local part is a public telephone number is given by a
preceding `+' (the `+' would not be entered from a telephone keypad,
it is added by the system as a flag). Since the primary information
in the numeric scheme is contained by the digits, other character
separators (e.g. `-') may be ignored (i.e. to allow parsing of the
numeric local mailbox) or may be used to recognize distinct portions
of the telephone number (e.g. country code). The specification of
the local part of a VPIM address can be split into the four groups
described below:
1) mailbox number
- for use as a private numbering plan (any number of digits)
- e.g. 2722@lucent.com
2) mailbox number+extension
- for use as a private numbering plan with extensions
any number of digits, use of `+' as separator
- e.g. 2722+111@Lucent.com
3) +international number
- for international telephone numbers conforming to E.164
maximum of 15 digits
- e.g. +16137637582@vm.nortel.ca
4) - for international telephone numbers conforming to E.164
maximum of 15 digits, with an extension (e.g. behind a
PBX) that has a maximum of 15 digits.
- e.g. +17035245550+230@ema.org
Note that this address format is designed to be compatible with
current usage within the voice messaging industry. It is not
compatible with the addressing formats of RFCs 2303-2304. It is
expected that as telephony services become more widespread on the
Internet, these addressing formats will converge.
Special addresses are provided for compatibility with the conventions
of Internet mail. These addresses do not use numeric local
addresses, both to conform to current Internet practice and to avoid
conflict with existing numeric addressing plans. Two special
addresses are RESERVED for use as follows:
postmaster@domain
By convention, a special mailbox named "postmaster" MUST exist on all
systems. This address is used for diagnostics and should be checked
regularly by the system manager. This mailbox is particularly likely
Vaudreuil & Parsons Standards Track [Page 7]
RFC 2421 VPIM v2 September 1998
to receive text messages, which is not normal on a voice processing
platform. The specific handling of these messages is an individual
implementation choice.
non-mail-user@domain
If a reply to a message is not possible, such as a telephone
answering message, then the special address "non-mail-user" must be
used as the originator's address. Any text name such as "Telephone
Answering", or the telephone number if it is available, is permitted.
This special address is used as a token to indicate an unreachable
originator. For compatibility with the installed base of mail user
agents, implementations that generate this special address MUST send
a negative delivery status notification (DSN) for reply messages sent
to the undeliverable address. The status code for such NDN's is
5.1.1 "Mailbox does not exist".
Example:
From: Telephone Answering <non-mail-user@mycompany.com>
There are many ways to handle distribution list (DL) expansions and
none are 'standard'. Simple alias is a behavior closest to what most
voice mail systems do today and what is to be used with VPIM
messages. That is:
Reply to the originator - (Address in the RFC822 Reply-to or From
field)
Errors to the submitter - (Address in the MAIL FROM: field of the
ESMTP exchange and the Return-Path:
RFC 822 field)
Some proprietary voice messaging protocols include only the recipient
of the particular copy in the envelope and include no "header fields"
except date and per-message features. Most voice messaging systems
do not provide for "Header Information" in their messaging queues and
only include delivery information. As a result, recipient
information MAY be in either the To or CC header fields. If all
recipients cannot be presented (e.g. unknown DL expansion) then the
recipient header fields MUST be omitted to indicate that an accurate
list of recipients (e.g. for use with a reply-all capability) is not
known.
Vaudreuil & Parsons Standards Track [Page 8]
RFC 2421 VPIM v2 September 1998
Internet messages contain a header information block. This header
block contains information required to identify the sender, the list
of recipients, the message send time, and other information intended
for user presentation. Except for specialized gateway and mailing
list cases, header fields do not indicate delivery options for the
transport of messages.
Distribution list processors are noted for modifying or adding to the
header fields of messages that pass through them. VPIM systems MUST
be able to accept and ignore header fields that are not defined here.
The following header lines are permitted for use with VPIM voice
messages:
The originator's fully-qualified domain address (a mailbox address
followed by the fully-qualified domain name). The user listed in
this field should be presented in the voice message envelope as the
originator of the message.
Systems compliant with this profile SHOULD provide the text personal
name of the voice message originator in a quoted phrase, if the name
is available. Text names of corporate or positional mailboxes MAY be
provided as a simple string. From [RFC822]
Example:
From: "Joe S. User" <12145551212@mycompany.com>
From: Technical Support <611@serviceprovider.com>
The From address SHOULD be used for replies (see 4.6). However, if
the From address contains <non-mail-user@domain>, the user SHOULD NOT
be offered the option to reply, nor should notifications be sent to
this address.
Voice mail machines may not be able to support separate attributes
for the FROM, REPLY-TO, and SENDER header field and the SMTP MAIL
FROM command, VPIM conforming systems SHOULD set these values to the
same address. Use of addresses different than those present in the
From header field address may result in unanticipated behavior.
Vaudreuil & Parsons Standards Track [Page 9]
RFC 2421 VPIM v2 September 1998
The To header contains the recipient's fully-qualified domain
address. There may be one or more To: fields in any message.
Example:
To: +12145551213@mycompany.com
Systems compliant to this profile SHOULD provide a list of recipients
only if all recipients are provided. The To header MUST NOT be
included in the message if the sending message transport agent (MTA)
cannot resolve all the addresses in it, e.g. if an address is a DL
alias for which the expansion is unknown (see 4.1.3). If present,
the addresses in the To header MAY be used for a reply message to all
recipients.
Systems compliant to this profile MAY also discard the To addresses
of incoming messages because of the inability to store the
information. This would, of course, make a reply-to-all capability
impossible.
The cc header contains additional recipients' fully-qualified domain
addresses. Many voice mail systems maintain only sufficient envelope
information for message delivery and are not capable of storing or
providing a complete list of recipients.
Systems compliant to this profile SHOULD provide a list of recipients
only if all disclosed recipients can be provided. The list of
disclosed recipients does not include those sent via a blind copy. If
not, systems SHOULD omit the To and Cc header fields to indicate that
the full list of recipients is unknown.
Example:
Cc: +12145551213@mycompany.com
Systems compliant to this profile MAY discard the Cc addresses of
incoming messages as necessary. If a list of Cc or to addresses is
present, these addresses MAY be used for a reply message to all
recipients.
Vaudreuil & Parsons Standards Track [Page 10]
RFC 2421 VPIM v2 September 1998
The Date header contains the date, time, and time zone in which the
message was sent by the originator. The time zone SHOULD be
represented in a four-digit time zone offset, such as -0500 for North
American Eastern Standard Time. This may be supplemented by a time
zone name in parentheses, e.g., "-0900 (PDT)". Compliant
implementations SHOULD be able to convert RFC 822 date and time
stamps into local time.
Example:
Date: Wed, 28 Jul 96 10:08:49 -0800 (PST)
The sending system MUST report the time the message was sent. If the
VPIM sender is relaying a message from a system which does not
provide a time stamp, the time of arrival at the VPIM system SHOULD
be used as the date. From [RFC822]
The Sender header field contains the actual address of the originator
if the message is sent by an agent on behalf of the author indicated
in the From: field. This header field MAY be sent by VPIM conforming
system. If it is present in a VPIM message, the receiving VPIM
implementation may ignore the field and only present the From header
field.
The Return-path header is added by the final delivering SMTP server.
If present, it contains the address from the MAIL FROM parameter of
the ESMTP exchange (see 5.1.2). Any error messages resulting from the
delivery failure MUST be sent to this address (see [DRPT] for
additional details). Note that if the Return-path is null ("<>"),
e.g. no path, loop prevention or confidential, a notification MUST
NOT be sent. If the Return path address is not available (either
from this header or the MAIL FROM parameter) the From address may be
used to deliver notifications.
The Message-id header contains a unique per-message identifier. A
unique message-id MUST be generated for each message sent from a
compliant implementation.
The message-id is not required to be stored on the receiving system.
This identifier MAY be used for tracking, auditing, and returning
Vaudreuil & Parsons Standards Track [Page 11]
RFC 2421 VPIM v2 September 1998
receipt notification reports. From [RFC822]
Example:
Message-id: <12345678@mycompany.com>
If present, the reply-to header provides a preferred address to which
reply messages should be sent (see 4.6). Typically, voice mail
systems can only support one originator of a message so it is
unlikely that this field can be supported. A compliant system SHOULD
NOT send a Reply-To header. However, if a reply-to header is present,
a reply-to sender message MAY be sent to the address specified (that
is, overwriting From). From [RFC822] This preferred address of the
originator must also be provided in the originator's vCard EMAIL
attribute, if present (see 4.3.3).
The Received header contains trace information added to the beginning
of a RFC 822 message by MTAs. This is the only header permitted to
be added by an MTA. Information in this header is useful for
debugging when using an US-ASCII message reader or a header parsing
tool.
A compliant system MUST add Received header fields when acting as a
gateway and MUST NOT remove any Received fields when relaying
messages to other MTAs or gateways.. These header fields MAY be
ignored or deleted when the message is received at the final
destination. From [RFC822]
The MIME-Version header indicates that the message conforms to the
MIME message format specification. Systems compliant with this
specification SHOULD include a comment with the words "(Voice 2.0)".
RFC 1911 defines an earlier version of this profile and uses the
token (Voice 1.0). From [MIME1][VPIM1]
Example:
MIME-Version: 1.0 (Voice 2.0)
This identifier is intended for information only and SHOULD NOT be
used to semantically identify the message as being a VPIM message.
Instead, the presence of the content defined in [V-MSG] SHOULD be
used if identification is necessary.
Vaudreuil & Parsons Standards Track [Page 12]
RFC 2421 VPIM v2 September 1998
The content-type header declares the type of content enclosed in the
message. The typical top level content in a VPIM Message SHOULD be
multipart/voice-message, a mechanism for bundling several components
into a single identifiable voice message. The allowable contents are
detailed in section 4.3 of this document. From [MIME2]
Because Internet mail was initially specified to carry only 7-bit
US-ASCII text, it may be necessary to encode voice and fax data into
a representation suitable for that environment. The content-
transfer-encoding header describes this transformation if it is
needed. Compliant implementations MUST recognize and decode the
standard encodings, "Binary", "7bit, "8bit", "Base64" and "Quoted-
Printable". The allowable content-transfer-encodings are specified
in section 4.3. From [MIME1]
The sensitivity header, if present, indicates the requested privacy
level. The case-insensitive values "Personal" and "Private" are
specified. If no privacy is requested, this field is omitted.
If a sensitivity header is present in the message, a compliant system
MUST prohibit the recipient from forwarding this message to any other
user. A compliant system, however, SHOULD allow the responder to
reply to a sensitive message, but SHOULD NOT include the original
message content. The sensitivity of the reply message MAY be set by
the responder.
If the receiving system does not support privacy and the sensitivity
is one of "Personal" or "Private", a negative delivery status
notification must sent to the originator with the appropriate status
code indicating that privacy could not be assured. The message
contents SHOULD be returned to the sender to allow for a voice
context with the notification. A non-delivery notification to a
private message SHOULD NOT be tagged private since it will be sent to
the originator. From: [X.400]
Indicates the requested importance to be given by the receiving
system. The case-insensitive values "low", "normal" and "high" are
specified. If no special importance is requested, this header may be
omitted and the value assumed to be "normal".
Vaudreuil & Parsons Standards Track [Page 13]
RFC 2421 VPIM v2 September 1998
Compliant implementations MAY use this header to indicate the
importance of a message and may order messages in a recipient's
mailbox. From: [X.400]
The subject field is often provided by email systems but is not
widely supported on Voice Mail platforms. For compatibility with text
based mailbox interfaces, a text subject field SHOULD be generated by
a compliant implementation but MAY be discarded if present by a
receiving system. From [RFC822]
It is recommended that voice messaging systems that do not support
any text user interfaces (e.g. access only by a telephone) insert a
generic subject header of "VPIM Message" for the benefit of text
enabled recipients.
This header MAY be present to indicate that the sender is requesting
a receipt notification from the receiving user agent. This message
disposition notification (MDN) is typically sent by the user agent
after the user has listened to the message and consented to an MDN
being sent
Example:
Disposition-notification-to: +12145551213@mycompany.com
The presence of a Disposition-notification-to header in a message is
merely a request for an MDN described in 4.4.5. The recipients' user
agents are always free to silently ignore such a request so this
header does not burden any system that does not support it. From
[MDN].
This header MAY be present to define future extensions parameters for
an MDN requested by the presence of the header in the previous
section. Currently no parameters are defined by this document or by
[MDN]. However, this header MUST be parsed if present, if MDNs are
supported. If it contains a extension parameter that is required for
proper MDN generation (noted with "=required"), then an MDN MUST NOT
be sent if the parameter is not understood. See [MDN] for complete
details.
Vaudreuil & Parsons Standards Track [Page 14]
RFC 2421 VPIM v2 September 1998
Example:
Disposition-notification-options:
whizzbang=required,foo
MIME, introduced in [MIME1], is a general-purpose message body format
that is extensible to carry a wide range of body parts. It provides
for encoding binary data so that it can be transported over the 7-bit
text-oriented SMTP protocol. This transport encoding (denoted by the
Content-Transfer-Encoding header field) is in addition to the audio
encoding required to generate a binary object.
MIME defines two transport encoding mechanisms to transform binary
data into a 7 bit representation, one designed for text-like data
("Quoted-Printable"), and one for arbitrary binary data ("Base64").
While Base64 is dramatically more efficient for audio data, either
will work. Where binary transport is available, no transport
encoding is needed, and the data can be labeled as "Binary".
An implementation in compliance with this profile SHOULD send audio
and/or facsimile data in binary form when binary message transport is
available. When binary transport is not available, implementations
MUST encode the audio and/or facsimile data as Base64. The detection
and decoding of "Quoted-Printable", "7bit", and "8bit" MUST be
supported in order to meet MIME requirements and to preserve
interoperability with the fullest range of possible devices.
However, if a content is received in a transfer encoding that cannot
be rendered to the user, an appropriate negative delivery status
notification MUST be sent.
The content types described in this section are identified for use
within the multipart/voice-message content. This content, which is
the fundamental part of a VPIM message, is referred to as a VPIM
voice message in this document.
Only the contents profiled subsequently can be sent within a VPIM
voice message construct (i.e., the mulitpart/voice-message content
type) to form a simple or a more complex structure (several examples
are given in Appendix B). The presence of other contents within a
VPIM voice message is an error condition and SHOULD result in a
negative delivery status notification. When multiple contents are
present within the multipart/voice-message, they SHOULD be presented
to the user in the order that they appear in the message.
Vaudreuil & Parsons Standards Track [Page 15]
RFC 2421 VPIM v2 September 1998
This MIME multipart structure provides a mechanism for packaging a
voice message into one container that is tagged as VPIM v2 compliant.
The semantic of multipart/Voice-Message (defined in [V-MSG]) is
identical to multipart/mixed and may be interpreted as that by
systems that do not recognize this content-type.
The Multipart/Voice-Message content-type MUST only contain the
profiled media and content types specified in this section (i.e.
audio/*, image/*, message/rfc822 and text/directory). The most
common will be: spoken name, spoken subject, the message itself,
attached fax and directory info. Forwarded messages are created by
simply using the message/rfc822 construct.
Conformant implementations MUST send the multipart/voice-message in a
VPIM message. In most cases, this Multipart/Voice-Message content
will be the top level (i.e. in the Content-Type header). Conformant
implementations MUST recognize the Multipart/Voice-Message content
(whether it is a top level content or below a multipart/mixed) and be
able to separate the contents (e.g. spoken name or spoken subject).
MIME requires support of the Message/RFC822 message encapsulation
body part. This body part is used within a multipart/voice-message
to forward complete messages (see 4.5) or to reply with original
content (see 4.6). From [MIME2]
This content allows for the inclusion of a Versit vCard [VCARD]
electronic business card within a VPIM message. The format is
suitable as an interchange format between applications or systems,
and is defined independent of the method used to transport it. It
provides a useful mechanism to transport information about the
originator that can be used by the receiving VPIM system (see 6) or
other local applications
Each vCard MUST be contained within a Text/Directory content type
[MIMEDIR] within a VPIM message. [MIMEDIR] requires that the
character set MUST be defined as a parameter value (typically us-
ascii for VPIM) and that the profile SHOULD be defined (the value
MUST be vCard within VPIM messages).
Each VPIM message SHOULD be created with a Text/Directory (vCard
profile) content type that MUST contain the preferred email address,
telephone number, and text name of the message originator as well as
Vaudreuil & Parsons Standards Track [Page 16]
RFC 2421 VPIM v2 September 1998
the vCard version. The vCard SHOULD contain the spoken name and role
of the originator, as well as the revision date. Any other vCard
attribute MAY also be present. The intent is that the vCard be used
as the source of information to contact the originator (e.g., reply,
call).If the text/directory content-type is included in a VPIM
message, the vCard profile [VCARD] MUST be used and MUST specify at
least the following attributes:
TEL - Public switched telephone number in international (E.164)
format (various types, typically VOICE)
EMAIL - email address (various types, typically INTERNET; the
type VPIM is optionally used to denote an address that
supports VPIM messages(see 18.1))
VERSION - Indicates the version of the vCard profile. Version 3.0
[VCARD] MUST be used.
The following attributes SHOULD be specified:
N - Family Name, Given Name, Additional Names, Honorific
Prefixes, and Suffixes. Because it is expected that
recipients using a telephone user interface will use the
information in the vCard to identify the originator, and
the GUI will see the information presented in the FROM
line, all present components in the text name of the FROM
header field MUST match the values provided by the Vcard.
ROLE - The role of the person identified in `N' or `FN', but may
also be used to distinguish when the sender is a corporate
or positional mailbox
SOUND - spoken name sound data (various types, typically 32KADPCM)
REV - Revision of vCard in ISO 8601 date format
The vCard MAY use other attributes as defined in [VCARD] or
extensions attributes not yet defined (e.g. capabilities).
If present, the spoken name attribute MUST be denoted by a content ID
pointing to an audio/* content elsewhere in the VPIM message.
A typical VPIM message (i.e. no forwarded parts), MUST only contain
one vCard -- more than one is an error condition. A VPIM message
that contains forwarded messages, though, may contain multiple
vCards. However, these vCards MUST be associated with the
originator(s) of the forwarded message(s) and the originator of the
forwarding message. As a result, all forwarded vCards will be
Vaudreuil & Parsons Standards Track [Page 17]
RFC 2421 VPIM v2 September 1998
contained in message/rfc822 contents -- only the vCard of forwarding
originator will be at the top-level.
Example:
Content-Type: text/directory; charset=us-ascii; profile=vCard
Content-Transfer-Encoding: 7bit
BEGIN:VCARD
N:Parsons;Glenn
ORG:Northern Telecom
TEL;TYPE=VOICE;MSG;WORK:+1-613-763-7582
EMAIL;TYPE=INTERNET;glenn.parsons@nortel.ca
EMAIL;TYPE=INTERNET;VPIM:6137637582@vm.nortel.ca
SOUND;TYPE=32KADPCM;ENCODING=URI: CID:<part1@VM2-4321>
REV:19960831T103310Z
VERSION: 3.0
END:VCARD
An implementation compliant to this profile MUST send Audio/32KADPCM
by default for voice [ADPCM]. Receivers MUST be able to accept and
decode Audio/32KADPCM. Typically this body contains several minutes
of message content, however if used for spoken name or subject the
content should be considerably shorter (i.e. about 10 and 20 seconds
respectively).
If an implementation can only handle one voice body, then multiple
voice bodies (if present) SHOULD be concatenated, and SHOULD NOT be
discarded. It is RECOMMENDED that this be done in the same order as
they were sent. Note that if an Originator Spoken Name audio body and
a vCard are both present in a VPIM message, the vCard SOUND attribute
MUST point to this audio body (see 4.3.3).
While any valid MIME body header MAY be used, several header fields
have the following semantics when included with this body part:
This field MAY be present to facilitate the text identification of
these body parts in simple email readers. Any values may be used,
though it may be useful to use values similar to those for Content-
Disposition.
Example:
Content-Description: Big Telco Voice Message
Vaudreuil & Parsons Standards Track [Page 18]
RFC 2421 VPIM v2 September 1998
This field MUST be present to allow the parsable identification of
these body parts. This is especially useful if, as is typical, more
than one Audio/32KADPCM body occurs within a single level (e.g.
multipart/voice-message). Since a VPIM voice message is intended to
be automatically played upon display of the message, in the order in
which the audio contents occur, the audio contents must always be of
type inline. However, it is still useful to include a filename
value, so this should be present if this information is available.
From [DISP]
In order to distinguish between the various types of audio contents
in a VPIM voice message a new disposition parameter "voice" is
defined with the parameter values below to be used as appropriate
(see 18.2):
Voice-Message - the primary voice message,
Voice-Message-Notification - a spoken delivery notification
or spoken disposition notification,
Originator-Spoken-Name - the spoken name of the originator,
Recipient-Spoken-Name - the spoken name of the recipient if
available to the originator and present if there is ONLY one
recipient,
Spoken-Subject- the spoken subject of the message, typically
spoken by the originator
Note that there SHOULD only be one instance of each of these types of
audio contents per message level. Additional instances of a given
type (i.e., parameter value) may occur within an attached forwarded
voice message.
Implementations that do not understand the "voice" parameter (or the
Content-Disposition header) can safely ignore it, and will present
the audio bodyparts in order (but will not be able to distinguish
between them).
Example:
Content-Disposition: inline; voice=spoken-subject;
filename="msg001.726"
This field MAY be present to allow the specification of the length of
the audio bodypart in seconds. The use of this field on reception is
a local implementation issue. From [DUR]
Vaudreuil & Parsons Standards Track [Page 19]
RFC 2421 VPIM v2 September 1998
Example:
Content-Duration: 33
This field MAY be present to allow the specification of the spoken
language of the audio bodypart. The encoding is defined in [LANG].
The use of this field on reception is a local implementation issue.
Example for UK English:
Content-Language: en-UK
A common image encoding for facsimile, known as TIFF-F, is a
derivative of the Tag Image File Format (TIFF) and is described in
several documents. For the purposes of VPIM, the F Profile of TIFF
for Facsimile (TIFF-F) is defined in [TIFF-F] and the image/tiff MIME
content type is defined in [TIFFREG]. While there are several
formats of TIFF, only TIFF-F is profiled for use in a VPIM voice
message. Further, since the TIFF-F file format is used in a store-
and-forward mode with VPIM, the image MUST be encoded so that there
is only one image strip per facsimile page.
All VPIM implementations that support facsimile SHOULD generate
TIFF-F compatible facsimile contents in the image/tiff;
application=faxbw sub-type encoding by default. An implementation
MAY send this fax content in VPIM voice messages and MUST be able to
recognize and display it in received messages. If a fax message is
received that cannot be rendered to the user (e.g. the receiving VPIM
system does not support fax), then the system MUST return the message
with a negative delivery status notification with a media not
supported status code.
While any valid MIME body header MAY be used (e.g., Content-
Disposition to indicate the filename), none are specified to have
special semantics for VPIM and MAY be ignored. Note that the content
type parameter application=faxbw MUST be included in outbound
messages. However, inbound messages with or without this parameter
MUST be rendered to the user (if the rendering software encounters an
error in the file format, some form of negative delivery status
notification MUST be sent to the originator).
Vaudreuil & Parsons Standards Track [Page 20]
RFC 2421 VPIM v2 September 1998
Proprietary voice or fax encoding formats or other standard formats
MAY be supported under this profile provided a unique identifier is
registered with the IANA prior to use (see [MIME4]). The voice
encodings should be registered as sub-types of Audio and the fax
encodings should be registered as sub-types of Image
Use of any other encoding except audio/32kadpcm or image/tiff;
application=faxbw reduces interoperability in the absence of explicit
manual system configuration. A compliant implementation MAY use any
other encoding with explicit per-destination configuration.
An implementation compliant with this profile MAY send additional
contents in a VPIM message, but ONLY outside of the multipart/voice-
message. The content types described in this section are identified
for use with this profile. Additional contents not defined in this
profile MUST NOT be used without prior explicit per-destination
configuration. If an implementation receives a VPIM message that
contains content types not specified in this profile, their handling
is a local implementation issue (e.g. the unknown contents MAY be
discarded if they cannot be presented to the recipient). Conversely,
if an implementation receives a non-VPIM message (i.e., without a
mulitpart/voice-message content type) with any of the contents
defined in 4.3 & 4.4, it SHOULD deliver those contents, but the full
message handling is a local issue (e.g. the unknown contents _or_ the
entire message MAY be discarded). Implementations MUST issue
negative delivery status notifications to the originator when any
form of non-delivery to the recipient occurs.
The multipart contents defined below MAY be sent as the top level of
a VPIM message (with other noted contents below them as required.) As
well, the multipart/mixed content SHOULD be used as the top level of
a VPIM message to form a more complex structure (e.g., with
additional content types). When multiple contents are present, they
SHOULD be presented to the user in the order that they appear in the
message. Several examples are given in Appendix B.
MIME provides the facilities for enclosing several body parts in a
single message. Multipart/Mixed SHOULD only be used for sending
complex voice or multimedia messages. That is, as the top level
Content-Type when sending one of the following contents (in addition
to the VPIM voice message) in a VPIM message. Compliant systems MUST
accept multipart/mixed body parts. From [MIME2]
Vaudreuil & Parsons Standards Track [Page 21]
RFC 2421 VPIM v2 September 1998
MIME requires support of the basic Text/Plain content type. This
content type has limited applicability within the voice messaging
environment. However, because VPIM is a MIME profile, MIME
requirements should be met. Compliant VPIM implementations SHOULD
NOT send the Text/Plain content-type. Compliant implementations MUST
accept Text/Plain messages, however, specific handling is left as an
implementation decision. From [MIME2]
There are several mechanisms that can be used to support text (once
accepted) on voice messaging systems including text-to-speech and
text-to-fax conversions. If no rendering of the text is possible
(i.e., it is not possible for the recipient to determine if the text
is a critical part of the message), the entire message MUST be
returned to the sender with a negative delivery status notification
and a media-unsupported status code.
The Multipart/Report is used for enclosing human-readable and machine
parsable notification (e.g. Message/delivery-status) body parts and
any returned message content. The multipart/report content-type is
used to deliver both delivery status reports indicating transport
success or failure and message disposition notifications to indicate
post-delivery events such as receipt notification. Compliant
implementations MUST use the Multipart/Report construct. Compliant
implementations MUST recognize and decode the Multipart/Report
content type and its components in order to present the report to the
user. From [REPORT]
Multipart/Report messages from VPIM implementations SHOULD include
the human-readable description of the error as a spoken audio/*
content (this speech SHOULD also be made available to the
notification recipient). As well, VPIM implementations MUST be able
to handle (and MAY generate) Multipart/Report messages that encode
the human-readable description of the error as text. Note that per
[DSN] the human-readable part MUST always be present.
This MIME body part is used for sending machine-parsable delivery
status notifications. Compliant implementations MUST use the
Message/delivery-status construct when returning messages or sending
warnings. Compliant implementations MUST recognize and decode the
Message/delivery-status content type and present the reason for
failure to the sender of the message. From [DSN]
Vaudreuil & Parsons Standards Track [Page 22]
RFC 2421 VPIM v2 September 1998
This MIME body part is used for sending machine-parsable receipt
notification message disposition notifications. Conforming
implementations SHOULD use the Message/Disposition-notification
construct when sending post-delivery message status notifications.
These MDNs, however, MUST only be sent in response to the presence of
the Disposition-notification-to header in 4.2.16. Conforming
implementations should recognize and decode the Message/Disposition-
notification content type and present the notification to the user.
From [MDN]
VPIM version 2 explicitly supports the forwarding of voice and fax
content with voice or fax annotation. However, only the two
constructs described below are acceptable in a VPIM message. Since
only the first (i.e. message/rfc822) can be recognized as a forwarded
message (or even multiple forwarded messages), it is RECOMMENDED that
this construct be used whenever possible.
Forwarded VPIM messages SHOULD be sent as a multipart/voice-message
with the entire original message enclosed in a message/rfc822 content
type and the annotation as a separate Audio/* or image/* body part.
If the RFC822 header fields are not available for the forwarded
content, simulated header fields with available information SHOULD be
constructed to indicate the original sending timestamp, and the
original sender as indicated in the "From" line. However, note that
at least one of "From", "Subject", or "Date" MUST be present. As
well, the message/rfc822 content MUST include at least the "MIME-
Version", and "Content-Type" header fields. From [MIME2]
In the event that forwarding information is lost through
concatenation of the original message and the forwarding annotation,
such as must be done in a gateway between VPIM and the AMIS voice
messaging protocol, the entire audio content MAY be sent as a single
Audio/* segment without including any forwarding semantics.
Replies to VPIM messages (and Internet mail messages) are addressed
to the address noted in the reply-to header (see 4.2.8) if it is
present, else the From address (see 4.2.1) is used. The vCard EMAIL
attribute, if present, SHOULD be the same as the reply-to address and
may be the same as the From address. While the vCard is the senders
preferred address it SHOULD NOT be used to generate a reply. Also,
the Return-path address should not be used for replies.
Vaudreuil & Parsons Standards Track [Page 23]
RFC 2421 VPIM v2 September 1998
Support of multiple originator header fields is often not possible on
voice messaging systems, so it may be necessary to choose only one
when gatewaying a VPIM message to another voice message system.
However, implementers should note that this may make it impossible to
send error messages and replies to their proper destinations.
In some cases, a reply message is not possible, such as with a
message created by telephone answering (i.e. classic voice mail). In
this case, the From field MUST contain the special address non-mail-
user@domain (see 4.1.2). A null ESMTP MAIL FROM address SHOULD also
be used in this case (see 5.1.2). A receiving VPIM system SHOULD NOT
offer the user the option to reply to this kind of message.
VPIM delivery status notification messages (4.4.4) MUST be sent to
the originator of the message when any form of non-delivery of the
subject message or its components occurs. These error messages must
be sent to the return path (4.2.6) if present, otherwise, the From
(4.2.1) address may be used.
VPIM Receipt Notification messages (4.4.5) should be sent to the
sender specified in the Disposition-Notification-To header field
(4.2.16), only after the message has been presented to the recipient
or if the message has somehow been disposed of without being
presented to the recipient (e.g. if it were deleted before playing
it).
VPIM Notification messages may be positive or negative, and can
indicate delivery at the server or receipt by the client. However,
the notification MUST be contained in a multipart/report container
(4.4.3) and SHOULD contain a spoken error message.
If a VPIM system receives a message with contents that are not
understood (see 4.3 & 4.4), its handling is a local matter. A
delivery status notification SHOULD be generated if the message could
not be delivered because of unknown contents (e.g., on traditional
voice processing systems). In some cases, the message may be
delivered (with a positive DSN sent) to a mailbox before the
determination of rendering can be made.
Messages are transported between voice mail machines using the
Internet Extended Simple Mail Transfer Protocol (ESMTP). All
information required for proper delivery of the message is included
in the ESMTP dialog. This information, including the sender and
recipient addresses, is commonly referred to as the message
Vaudreuil & Parsons Standards Track [Page 24]
RFC 2421 VPIM v2 September 1998
"envelope". This information is equivalent to the message control
block in many analog voice messaging protocols.
ESMTP is a general-purpose messaging protocol, designed both to send
mail and to allow terminal console messaging. Simple Mail Transport
Protocol (SMTP) was originally created for the exchange of US-ASCII
7-bit text messages. Binary and 8-bit text messages have
traditionally been transported by encoding the messages into a 7-bit
text-like form. [ESMTP] formalized an extension mechanism for SMTP,
and subsequent RFCs have defined 8-bit text networking, command
streaming, binary networking, and extensions to permit the
declaration of message size for the efficient transmission of large
messages such as multi-minute voice mail.
The following sections list ESMTP commands, keywords, and parameters
that are required and those that are optional for conformance to this
profile.
Base SMTP greeting and identification of sender. This command is not
to be sent by compliant systems unless the more-capable EHLO command
is not accepted. It is included for compatibility with general SMTP
implementations. Compliant servers MUST implement the HELO command
for backward compatibility but clients SHOULD NOT send it unless EHLO
is not supported. From [SMTP]
Originating mailbox. This address contains the mailbox to which
errors should be sent. VPIM implementations SHOULD use the same
address in the MAIL FROM command as is used in the From header field.
This address is not necessarily the same as the message Sender listed
in the message header fields if the message was received from a
gateway or sent to an Internet-style mailing list. From [SMTP, ESMTP]
The MAIL FROM address SHOULD be stored in the local message store for
the purposes of generating a delivery status notification to the
originator. The address indicated in the MAIL FROM command SHOULD be
passed as a local system parameter or placed in a Return-Path: line
inserted at the beginning of a VPIM message. From [HOSTREQ]
Since delivery status notifications MUST be sent to the MAIL FROM
address, the use of the null address ("<>") is often used to prevent
looping of messages. This null address MAY be used to note that a
particular message has no return path (e.g. a telephone answer
Vaudreuil & Parsons Standards Track [Page 25]
RFC 2421 VPIM v2 September 1998
message). From [SMTP]
Recipient's mailbox. The parameter to this command contains only the
address to which the message should be delivered for this
transaction. It is the set of addresses in one or more RCPT TO
commands that are used for mail routing. From [SMTP, ESMTP]
Note: In the event that multiple transport connections to multiple
destination machines are required for the same message, the set of
addresses in a given transport connection may not match the list of
recipients in the message header fields.
Initiates the transfer of message data. Support for this command is
required. Compliant implementations MUST implement the SMTP DATA
command for backwards compatibility. From [SMTP]
Requests a change-of-roles, that is, the client that opened the
connection offers to assume the role of server for any mail the
remote machine may wish to send. Because SMTP is not an
authenticated protocol, the TURN command presents an opportunity to
improperly fetch mail queued for another destination. Compliant
implementations SHOULD NOT implement the TURN command. From [SMTP]
Requests that the connection be closed. If accepted, the remote
machine will reset and close the connection. Compliant
implementations MUST implement the QUIT command. From [SMTP]
Requests verification that this node can reach the listed recipient.
While this functionality is also included in the RCPT TO command,
VRFY allows the query without beginning a mail transfer transaction.
This command is useful for debugging and tracing problems. Compliant
implementations MAY implement the VRFY command. From [SMTP] (Note
that the implementation of VRFY may simplify the guessing of a
Vaudreuil & Parsons Standards Track [Page 26]
RFC 2421 VPIM v2 September 1998
recipient's mailbox or automated sweeps for valid mailbox addresses,
resulting in a possible reduction in privacy. Various implementation
techniques may be used to reduce the threat, such as limiting the
number of queries per session.) From [SMTP]
The enhanced mail greeting that enables a server to announce support
for extended messaging options. The extended messaging modes are
discussed in subsequent sections of this document. Compliant
implementations MUST implement the ESMTP command and return the
capabilities indicated later in this memo. From [ESMTP]
The BDAT command provides a higher efficiency alternative to the
earlier DATA command, especially for voice. The BDAT command provides
for native binary transport of messages. Compliant implementations
SHOULD support binary transport using the BDAT command [BINARY].
The "PIPELINING" keyword indicates ability of the receiving server to
accept new commands before issuing a response to the previous
command. Pipelining commands dramatically improves performance by
reducing the number of round-trip packet exchanges and makes it
possible to validate all recipient addresses in one operation.
Compliant implementations SHOULD support the command pipelining
indicated by this keyword. From [PIPE]
The "SIZE" keyword provides a mechanism by which the SMTP server can
indicate the maximum size message supported. Compliant servers MUST
provide size extension to indicate the maximum size message that can
be accepted. Clients SHOULD NOT send messages larger than the size
indicated by the server. Clients SHOULD advertise SIZE= when sending
messages to servers that indicate support for the SIZE extension.
From [SIZE]
Vaudreuil & Parsons Standards Track [Page 27]
RFC 2421 VPIM v2 September 1998
The "CHUNKING" keyword indicates that the receiver will support the
high-performance binary transport mode. Note that CHUNKING can be
used with any message format and does not imply support for binary
encoded messages. Compliant implementations MAY support binary
transport indicated by this capability. From [BINARY]
The "BINARYMIME" keyword indicates that the SMTP server can accept
binary encoded MIME messages. Compliant implementations MAY support
binary transport indicated by this capability. Note that support for
this feature requires support of CHUNKING. From [BINARY]
The "DSN" keyword indicates that the SMTP server will accept explicit
delivery status notification requests. Compliant implementations
MUST support the delivery notification extensions in [DRPT].
The "ENHANCEDSTATUSCODES" keyword indicates that an SMTP server
augments its responses with the enhanced mail system status codes
[CODES]. These codes can then be used to provide more informative
explanations of error conditions, especially in the context of the
delivery status notifications format defined in [DSN]. Compliant
implementations SHOULD support this capability. From [STATUS]
The current message is a binary encoded MIME messages. Compliant
implementations SHOULD support binary transport indicated by this
parameter. From [BINARY]
The RET parameter indicates whether the content of the message should
be returned. Compliant systems SHOULD honor a request for returned
content. From [DRPT]
Vaudreuil & Parsons Standards Track [Page 28]
RFC 2421 VPIM v2 September 1998
The ENVID keyword of the SMTP MAIL command is used to specify an
"envelope identifier" to be transmitted along with the message and
included in any DSNs issued for any of the recipients named in this
SMTP transaction. The purpose of the envelope identifier is to allow
the sender of a message to identify the transaction for which the DSN
was issued. Compliant implementations MAY use this parameter. From
[DRPT]
The NOTIFY parameter indicates the conditions under which a delivery
report should be sent. Compliant implementations MUST honor this
request. From [DRPT]
The ORCPT keyword of the RCPT command is used to specify an
"original" recipient address that corresponds to the actual recipient
to which the message is to be delivered. If the ORCPT esmtp-keyword
is used, it MUST have an associated esmtp-value, which consists of
the original recipient address, encoded according to the rules below.
Compliant implementations MAY use this parameter. From [DRPT]
The ESMTP extensions suggested or required for conformance to VPIM
fall into two categories. The first category includes features which
increase the efficiency of the transport system such as SIZE,
BINARYMIME, and PIPELINING. In the event of a downgrade to a less
functional transport system, these features can be dropped with no
functional change to the sender or recipient.
The second category of features are transport extensions in support
of new functions. DSN and EnhancedStatusCodes provide essential
improvements in the handling of delivery status notifications to
bring email to the level of reliability expected of Voice Mail. To
ensure a consistent level of service across an intranet or the global
Internet, it is essential that VPIM compliant ESMTP support the ESMTP
DSN extension at all hops between a VPIM originating system and the
recipient system. In the situation where a `downgrade' is unavoidable
a relay hop may be forced (by the next hop) to forward a VPIM message
without the ESMTP request for positive delivery status notification.
It is RECOMMENDED that the downgrading system should continue to
attempt to deliver the message, but MUST send an appropriate delivery
Vaudreuil & Parsons Standards Track [Page 29]
RFC 2421 VPIM v2 September 1998
notification to the originator, e.g. the message left an ESMTP host
and was sent (unreliably) via SMTP.
It is the responsibility of a VPIM system to provide the fully-
qualified domain name (FQDN) of the recipient based on the address
entered by the user (if the entered address is not already a FQDN).
This would typically be an issue on systems that offered only a
telephone user interface. The mapping of the dialed target number to
a routeable FQDN address allowing delivery to the destination system
can be accomplished through implementation-specific means.
To facilitate a local dial-by-name cache, an implementation may wish
to populate local directories with the first and last names, as well
as the address information extracted from received messages. It is
mandated that only address information from vCard attachments to VPIM
messages be used to populate such a directory when the vCard is
available. Addresses or names parsed from the header fields of VPIM
messages SHOULD NOT be used to populate directories as it only
provides partial data. Alternatively, bilateral agreements could be
made to allow the bulk transfer of vCards between systems.
The use of client/server desktop mailbox protocols like IMAP or POP
to retrieve VPIM messages from a IMAP or POP message store is
possible without any special modifications to this VPIM
specification. Email clients (and web browsers) typically have a
table for mapping from MIME type to displaying application. The
audio/*, image/tiff and text/directory contents can be configured so
that they invoke the correct player/recorder for rendering. In
addition with IMAP clients, the first multipart/mixed content (if
present) will not appear since it is a generic part. The user
instead will be presented with a message that has (for example) audio
and image contents.
The Internet protocols provide a mechanism for the management of
messaging systems, from the management of the physical network
through the management of the message queues. SNMP should be
supported on a compliant message machine.
Vaudreuil & Parsons Standards Track [Page 30]
RFC 2421 VPIM v2 September 1998
The digital interface to the VM and the TCP/IP protocols MAY be
managed. MIB II MAY be implemented to provide basic statistics and
reporting of TCP and IP protocol performance [MIB II].
VPIM is a messaging application which must be supported in several
environments and be supported on differing devices. These
environments include traditional voice processing systems, desktop
voice messaging systems, store and forward relays, and protocol
translation gateways.
In order to accommodate all environments, this document defines two
areas of conformance: transport and content.
Transport conformant systems will pass VPIM messages in a store and
forward manner with assured delivery notifications and without the
loss of information. It is expected that most store and forward
Internet mail based messaging systems will be VPIM transport
compliant.
Content conformant systems will generate and interpret VPIM messages.
Conformance in the generation of VPIM messages indicates that the
restrictions of this profile are honored. Only contents specified in
this profile or extensions agreed to by bilateral agreement may be
sent. Conformance in the interpretation of VPIM messages indicates
that all VPIM content types and constructs can be received; that all
mandatory VPIM content types can be decoded and presented to the
recipient in an appropriate manner; and that any unrenderable
contents result in the appropriate notification.
A summary of the compliance requirements is contained in Appendix A.
VPIM end systems are expected to be both transport and content
conformant. They should generate conforming content, reliably send
it to the next hop system, receive a message, decode the message and
present it to the user. Voice messaging systems and protocol
conversion gateways are considered end systems.
Relay systems are expected to be transport compliant in order to
receive and send conforming messages. However, they must also create
VPIM conforming delivery status notifications in the event of
delivery problems.
Vaudreuil & Parsons Standards Track [Page 31]
RFC 2421 VPIM v2 September 1998
Desktop Email clients that support VPIM and are expected to be
content conformant. Desktop email clients use various protocols and
API's for exchanging messages with the local message store and
message transport system. While these clients may benefit from VPIM
transport capabilities, specific client-server requirements are out-
of-scope for this document.
This document is a profile of existing Internet mail protocols. To
maintain interoperability with Internet mail, any security to be
provided should be part of the of the Internet security
infrastructure, rather than a new mechanism or some other mechanism
outside of the Internet infrastructure.
Both Internet mail and voice messaging have their own set of threats
and countermeasures. As such, this specification does not create any
security issues not already existing in the profiled Internet mail
and voice mail protocols themselves. This section attends only to
the set of additional threats which ensue from integrating the two
services.
The actual sender of the voice message might not be the same as that
specified in the Sender or From header fields of the message content
header fields or the MAIL FROM address from the SMTP envelope. In a
tightly constrained environment, sufficient physical and software
controls may be able to ensure prevention of this problem. In
addition, the recognition of the senders voice may provide confidence
of the sender's identity irrespective of that specified in Sender or
From. It should be recognized that SMTP implementations do not
provide inherent authentication of the senders of messages, nor are
sites under obligation to provide such authentication.
Assigning an Internet mail address to a voice mailbox opens the
possibility of receiving unsolicited messages (either text or voice
mail). Traditionally voice mail systems operated in closed
environments and were not susceptible to unknown senders. Voice mail
users have a higher expectation of mailbox privacy and may consider
such messages as a security breach. Many Internet mail systems are
choosing to block all messages from unknown sources in an attempt to
Vaudreuil & Parsons Standards Track [Page 32]
RFC 2421 VPIM v2 September 1998
curb this problem.
Users of voice messaging systems have an expectation of a level of
message privacy which is higher than the level provided by Internet
mail without security enhancements. This expectation of privacy by
users SHOULD be preserved as much as possible.
Sufficient physical and software control may be acceptable in
constrained environments. Further, the profile specified in this
document does not in any way preclude the use of any Internet object
or channel security protocol to encrypt, authenticate, or non-
repudiate the messages.
[8BIT] Klensin, J., Freed, N., Rose, M., Stefferud, E., and D.
Crocker, "SMTP Service Extension for 8bit-MIMEtransport", RFC
1426, February 1993.
[ADPCM] Vaudreuil, G., and G. Parsons, "Toll Quality Voice - 32
kbit/s ADPCM: MIME Sub-type Registration", RFC 2422,
September 1998.
[AMIS-A] Audio Messaging Interchange Specifications (AMIS) - Analog
Protocol Version 1, Issue 2, February 1992.
[AMIS-D] Audio Messaging Interchange Specifications (AMIS) - Digital
Protocol Version 1, Issue 3 August 1993.
[BINARY] Vaudreuil, G., "SMTP Service Extensions for Transmission of
Large and Binary MIME Messages", RFC 1830, October 1995.
[CODES] Vaudreuil, G., "Enhanced Mail System Status Codes", RFC 1893,
January 1996.
[MIMEDIR] Howes, T., Smith, M., and F. Dawson, "A MIME Content-Type
for Directory Information", RFC 2425, September 1998.
[DISP] Troost, R., and S. Dorner, "Communicating Presentation
Information in Internet Messages: The Content-Disposition
Header", RFC 2183, August 1997.
[DNS1] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, November 1987.
Vaudreuil & Parsons Standards Track [Page 33]
RFC 2421 VPIM v2 September 1998
[DNS2] Mockapetris, P., "Domain names - concepts and facilities", STD
13, RFC 1034, November 1987.
[DRPT] Moore, K., "SMTP Service Extensions for Delivery Status
Notifications", RFC 1891, January 1996.
[DSN] Moore, K., and G. Vaudreuil, "An Extensible Message Format for
Delivery Status Notifications", RFC 1894, January 1996.
[DUR] Vaudreuil, G., and G. Parsons, "Content Duration MIME Header
Definition", RFC 2424, September 1998.
[E164] CCITT Recommendation E.164 (1991), Telephone Network and ISDN
Operation, Numbering, Routing and Mobile Service - Numbering
Plan for the ISDN Era.
[ESMTP] Klensin, J., Freed, N., Rose, M., Stefferud, E., and D.
Crocker, "SMTP Service Extensions", RFC 1869, November 1995.
[G726] CCITT Recommendation G.726 (1990), General Aspects of Digital
Transmission Systems, Terminal Equipment - 40, 32, 24,16
kbit/s Adaptive Differential Pulse Code Modulation (ADPCM).
[HOSTREQ] Braden, R., "Requirements for Internet Hosts -- Application
and Support", STD 3, RFC 1123, October 1989.
[LANG] Alvestrand, H., "Tags for the Identification of Languages",
RFC 1766, March 1995.
[MDN] Fajman, R., "An Extensible Message Format for Message
Disposition Notifications", RFC 2298, March 1998.
[MIB II] Rose, M., "Management Information Base for Network
Management of TCP/IP-based internets: MIB-II", RFC 1158, May
1990.
[MIME1] Freed, N., and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part One: Format of Internet Message
Bodies", RFC 2045, November 1996.
[MIME2] Freed, N., and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part Two: Media Types", RFC 2046, November
1996.
[MIME3] Moore, K., "Multipurpose Internet Mail Extensions (MIME) Part
Three: Message Header Extensions for Non-ASCII Text", RFC
2047, November 1996.
Vaudreuil & Parsons Standards Track [Page 34]
RFC 2421 VPIM v2 September 1998
[MIME4] Freed, N., Klensin, J., and J. Postel, "Multipurpose
Internet Mail Extensions (MIME) Part Four: Registration
Procedures", RFC 2048, November 1996.
[MIME5] Freed, N., and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part Five: Conformance Criteria and
Examples", RFC 2049, November 1996.
[PIPE] Freed, N., and A. Cargille, "SMTP Service Extension for
Command Pipelining", RFC 1854, October 1995.
[REPORT] Vaudreuil, G., "The Multipart/Report Content Type for the
Reporting of Mail System Administrative Messages", RFC 1892,
January 1996.
[REQ] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[RFC822] Crocker, D., "Standard for the Format of ARPA Internet Text
Messages", STD 11, RFC 822, August 1982.
[SIZE] Klensin, J., Freed, N., and K. Moore, "SMTP Service Extensions
for Message Size Declaration", RFC 1870, November 1995.
[SMTP] Postel, J., "Simple Mail Transfer Protocol", STD 10, RFC 821,
August 1982.
[STATUS] Freed, N., "SMTP Service Extension for Returning Enhanced
Error Codes", RFC 2034, October 1996.
[TIFF-F] Parsons, G., and J. Rafferty, "Tag Image File Format:
Application F", RFC 2306, March 1998.
[TIFFREG] Parsons, G., Rafferty, J., and S. Zilles, "Tag Image File
Format: image/tiff - MIME sub-type registraion", RFC 2302,
March 1998.
[V-MSG] Vaudreuil, G., and G. Parsons, "VPIM Voice Message: MIME
Sub-type Registration", RFC 2423, September 1998.
[VCARD] Dawson, F., and T. Howes, "vCard MIME Directory Profile", RFC
2426, September 1998.
[VPIM1] Vaudreuil, G., "Voice Profile for Internet Mail", RFC 1911,
February 1996.
[X.400] Hardcastle-Kille, S., "Mapping between X.400(1988) / ISO
10021 and RFC 822", RFC 1327, May 1992.
Vaudreuil & Parsons Standards Track [Page 35]
RFC 2421 VPIM v2 September 1998
The authors would like to offer a special thanks to the Electronic
Messaging Association (EMA), especially the members of the Voice
Messaging Committee and the VPIM Work Group, for their support of the
VPIM specification and the efforts they have made to ensure its
success.
The EMA hosts the VPIM web page at http://www.ema.org/vpim.
The following common voice processing errors and their corresponding
status codes are given as examples. Text after the error codes are
intended only for reference to describe the error code.
Implementations should provide implementation specific informative
comments after the error code rather than the text below.
Error condition RFC 1893 Error codes
----------------------------- --------------------------------
Analog delivery failed 4.4.0 Persistent connection error
because remote system is busy - other
Analog delivery failed 4.4.1 Persistent protocol error
because remote system is - no answer from host
ring-no-answer
Remote system did not answer 5.5.5 Permanent protocol error
AMIS-Analog handshake ("D" in - wrong version
response to "C" at connect
time)
Mailbox does not exist 5.1.1 Permanent mailbox error
- does not exist
Mailbox full or over quota 4.2.2 Persistent mailbox error
- full
Disk full 4.3.1 Persistent system error
- full
Command out of sequence 5.5.1 Permanent protocol error
- invalid command
Frame Error 5.5.2 Permanent protocol error
- syntax error
Mailbox does not support FAX 5.6.1 Permanent media error
- not supported
Mailbox does not support TEXT 5.6.1 Permanent media error
- not supported
Sender is not authorized 5.7.1 Permanent security error
- sender not authorized
Vaudreuil & Parsons Standards Track [Page 50]
RFC 2421 VPIM v2 September 1998
Message marked private, but 5.3.3 Permanent system error
system is not private capable - not feature capable
The following common voice processing disposition conditions and
their corresponding MDN Disposition (which contains the disposition
mode, type and modifier, if applicable) are given as examples.
Implementers should refer to [MDN] for a full description of the
format of message disposition notifications.
Notification event MDN Disposition mode, type & modifier
------------------------------ -------------------------------------
Message played by recipient, manual-action/MDN-sent-automatically;
receipt automatically returned displayed
Message deleted from mailbox manual-action/MDN-sent-automatically;
by user without listening deleted
Message cleared when mailbox manual-action/MDN-sent-automatically;
deleted by admin deleted/mailbox-terminated
Message automatically deleted automatic-action/
when older than administrator MDN-sent-automatically; deleted/
set threshold expired
Message processed, however manual-action/MDN-sent-automatically;
audio encoding unknown - processed/error
unable to play to user Error: unknown audio encoding
Vaudreuil & Parsons Standards Track [Page 51]
RFC 2421 VPIM v2 September 1998
To: ietf-mime-directory@imc.org
Subject: Registration of new parameter for text/directory MIME type
EMAIL
Type name: EMAIL
Type purpose: To specify the electronic mail address for
communication with the object the vCard represents (defined in
[VCARD]).
Type encoding: 8bit
Type value: A single text value.
Type special notes: The type may include the type parameter "TYPE" to
specify the format or preference of the electronic mail address. The
TYPE parameter values previously defined include: "internet" to
indicate an Internet addressing type, "x400" to indicate a X.400
addressing type and "pref" to indicate a preferred-use email address
when more than one is specified. The value of "vpim" is defined to
indicate that the address specified supports VPIM messages. Other
IANA registered address type may also be specified. The default email
type is "internet". A non-standard value may also be specified.
Type example:
EMAIL;TYPE=internet,vpim:jqpublic@xyz.dom1.com
To: IANA@IANA.ORG
Subject: Registration of new Content-Disposition parameter
Content-Disposition parameter name: voice
Allowable values for this parameter:
Voice-Message - the primary voice message,
Voice-Message-Notification - a spoken delivery notification
or spoken disposition notification,
Originator-Spoken-Name - the spoken name of the originator,
Vaudreuil & Parsons Standards Track [Page 52]
RFC 2421 VPIM v2 September 1998
Recipient-Spoken-Name - the spoken name of the recipient if
available to the originator and present if there is ONLY one
recipient,
Spoken-Subject- the spoken subject of the message, typically
spoken by the originator
Description:
In order to distinguish between the various types of audio contents
in a VPIM voice message a new disposition parameter "voice" is
defined with the preceding values to be used as appropriate. Note
that there SHOULD only be one instance of each of these types of
audio contents per message level. Additional instances of a given
type (i.e., parameter value) may occur within an attached forwarded
voice message.
Vaudreuil & Parsons Standards Track [Page 53]
RFC 2421 VPIM v2 September 1998
The updated profile in this document is based on the experience of a
proof of concept demonstration of VPIM at EMA'96 in April 1996 and a
subsequent demonstration of products at EMA'97 in April 1997. This
version of the profile is significantly different from the previous
described in [VPIM1]. The changes are categorized as general,
content, transport and compliance. They are detailed below:
1. General
- All definitions are now contained in separate documents that are
referenced by this profile. The new documents include:
- a refined multipart/voice-message definition
- a refined (i.e., added nibble order) audio/32KADPCM definition
- the definitions of TIFF-F and image/tiff for fax images
- the Content-Duration definition
- Changed the Voice version to 2.0
- Added Table of Contents and more examples
- Various editorial updates to improve readability
- Added more security considerations
2. Content
- Modified multipart/voice-message content type by dropping the
positional dependence of contents while restricting its contents to
voice message specific content types
- Explicitly indicated other contents that may be present ina
multipart/mixed content type
- Explicitly defined the forwarding model using message/RFC822
- Explained the use of reply-to and from header fields for
addressing message replies
- Deprecated the special "loopback" address because of security
concerns and its use only for testing
Vaudreuil & Parsons Standards Track [Page 54]
RFC 2421 VPIM v2 September 1998
- Defined the non-mail-user reserved address to support the case in
which replies to the originator are not possible
- Eliminated the text name in the "To" and "CC" header fields.
Deprecated ordering of text names in the "From" header.
- Added support for facsimile using TIFF-F in an image/tiff;
application=faxbw content type
- Profiled vCard in the text/directory body part for transport of
directory information about the originator
- Loosened text restriction
- Added additional details on delivery and receipt notifications
- Added support for message disposition notifications, also known
as receipt notifications.
- Added suggested addressing formats
- Described handling of private messages
- Described the handling of non-profiled contents in VPIM messages
- Described the use of Content-Disposition to semantically identify
audio contents
3. Transport
- Moved binary support to optional
- Added optional ESMTP keywords for return of content, enhanced
status codes, original recipient, and envelope ID
- Described use of null MAIL FROM address
4. Compliance
- Added an explicit section on conformance specifying conformance
to content or transport
- Improved conformance table in Appendix A
Vaudreuil & Parsons Standards Track [Page 55]
RFC 2421 VPIM v2 September 1998
Copyright (C) The Internet Society (1998). All Rights Reserved.
This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph are
included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process must be
followed, or as required to translate it into languages other than
English.
The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns.
This document and the information contained herein is provided on an
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Vaudreuil & Parsons Standards Track [Page 56]