One document matched: draft-ema-vpim-vpimv2r2-00.txt
Network Working Group Greg Vaudreuil
Internet Draft Lucent Technologies
Expires in six months Glenn Parsons
Obsoletes: RFC 2421 Nortel Networks
June 24, 1999
Voice Profile for Internet Mail - version 2
<draft-ema-vpim-vpimv2r2-00.txt>
Status of this Memo
This document is an Internet-Draft and is in full conformance with all
provisions of Section 10 of RFC2026.
This document is an Internet Draft. Internet Drafts are working
documents of the Internet Engineering Task Force (IETF), its Areas, and
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Copyright Notice
Copyright (C) The Internet Society (1999). All Rights Reserved.
This Internet-Draft is in conformance with Section 10 of RFC2026.
Internet Draft VPIM v2 June 1, 1999
Overview
This document profiles Internet mail for voice messaging. It obsoletes
RFC 2421 which describes version 2 of the profile with less precision.
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 VPIM mailing list: <vpim-
l@ema.org>
Working Group Summary
This document is a deliverable of the draft charter of the IETF VPIM
BOF. This document is intended as a revision of VPIM v2 [RFC 2421] for
the purposes of elevating its maturity status. No protocol changes
should be made from RFC 2421 but this document is hoped to be a more
precise profile.
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Table of Contents
1. ABSTRACT..........................................................4
2. SCOPE.............................................................5
2.1 Voice Messaging System Limitations ..............................5
2.2 Design Goals ....................................................6
3. PROTOCOL RESTRICTIONS.............................................7
4. VOICE MESSAGE INTERCHANGE FORMAT..................................8
4.1 Message Addressing Formats ......................................8
4.2 Message Header Fields ..........................................11
4.3 MIME Audio Content Descriptions ................................18
4.4 Voice Message Content Types ....................................19
4.5 Other MIME Content Types .......................................24
4.6 Return and Notification Messages ...............................26
4.7 Forwarded Messages .............................................28
4.8 Reply Messages .................................................28
4.9 Notification Messages ..........................................29
5. MESSAGE TRANSPORT PROTOCOL.......................................30
5.1 ESMTP Commands .................................................30
5.2 ESMTP Keywords .................................................32
5.3 ESMTP Parameters - MAIL FROM ...................................33
5.4 ESMTP Parameters - RCPT TO .....................................34
5.5 ESMTP - SMTP Downgrading .......................................34
6. DIRECTORY ADDRESS RESOLUTION.....................................35
7. MANAGEMENT PROTOCOLS.............................................35
7.1 Network Management .............................................35
8. CONFORMANCE REQUIREMENTS.........................................36
9. SECURITY CONSIDERATIONS..........................................37
9.1 General Directive ..............................................37
9.2 Threats and Problems ...........................................37
9.3 Security Techniques ............................................38
10. REFERENCES.......................................................38
11. ACKNOWLEDGMENTS..................................................41
12. COPYRIGHT NOTICE.................................................41
13. AUTHORS' ADDRESSES...............................................42
14. APPENDIX A - VPIM REQUIREMENTS SUMMARY...........................43
15. APPENDIX B - EXAMPLE VOICE MESSAGES..............................51
16. APPENDIX C - EXAMPLE ERROR VOICE PROCESSING ERROR CODES..........57
17. APPENDIX D - EXAMPLE VOICE PROCESSING DISPOSITION TYPES..........58
18. APPENDIX E - IANA REGISTRATIONS..................................59
18.1 vCard EMAIL Type Definition for VPIM .........................59
18.2 Voice Content-Disposition Parameter Definition ...............59
19. APPENDIX F - CHANGE HISTORY: RFC 2421 (VPIM V2) TO THIS DOCUMENT.61
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1. Abstract
Voice messaging evolved as telephone answering service into a full send,
receive, and forward messaging paradigm with unique message features,
semantics and usage patterns. Voice messaging was introduced on special
purpose computers that interface to a telephone switch and provide call
answering and voice messaging services. Traditionally, messages sent
from one voice messaging system to another were transported using analog
networking protocols based on DTMF signaling and analog voice playback.
As the demand for networking increases, there was a need for a standard
high-quality digital protocol to connect these machines. VPIM has
sucessfully demonstated it's usefulness as this new standard. VPIM is
widely implemented and is seeing deployment in early adopter customer
networks. This document clarifies ambiguities found in the earlier
specification and is consistent with implementation practice. The
profile is referred to as VPIM (Voice Profile for Internet Mail) in this
document.
This second revision of the version 2 of obsoletes RFC 2421 which less
precisely describes version 2 of the profile.
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2. Scope
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.
2.1 Voice Messaging System Limitations
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.
2) Voice mail machines usually act as an integrated Message Transfer
Agent, Message Store and User Agent. There is typically 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.
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It should be noted that newer systems are based natively on SMTP/MIME
and do not suffer these limitations. In particular, some systems may
support media other than voice and fax.
2.2 Design Goals
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. 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 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.
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3. Protocol Restrictions
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. 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].
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4. Voice Message Interchange Format
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].
4.1 Message Addressing Formats
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.
4.1.1 VPIM Addresses
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).
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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 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)
+international number+extension
- 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 RFC s 2303-2304. It is expected that as
telephony services become more widespread on the Internet, these
addressing formats will converge.
4.1.2 Special Addresses
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
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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 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" SHOULD 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>
4.1.3 Distribution Lists
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 then the recipient header fields SHOULD be omitted to indicate
that an accurate list of recipients (e.g. for use with a reply-all
capability) is not known.
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4.2 Message Header Fields
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:
4.2.1 From
The originator's fully-qualified domain address (a mailbox address
followed by the fully-qualified domain name) MUST be present. The user
listed in this field should be presented in the voice message envelope
of the voice messaging system as the originator of the message.
SEND RULES
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>
From: Non-mail-user@myserver.mycompany.com
Voice mail machines may not be able to support separate attributes for
the "From:" and "Reply-To:" header fields, the SMTP MAIL FROM and the
vCard email attribute, 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.
RECEPTION RULES
The "From:" address SHOULD be used for replies (see 4.7.14.7.1).
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.
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4.2.2 To
The "To:" field contains the recipient's fully-qualified domain address.
There MAY be one or more "To:" fields in any message.
Example:
To: +12145551213@mycompany.com
SEND RULES
Systems SHOULD provide a list of recipients only if all recipients are
provided.
Systems such as gateways from protocols which do not indicate the
complete list of recipients SHOULD provide a "To:" line. Because these
systems cannot accurately enumerate all recipients in the "To:" headers,
no recipients should be enumerated.
Systems compliant to this profile MAY discard the addresses in the "To:"
fields if they are unable to store the information. This would, of
course, make a reply-to-all capability impossible. If present, the
addresses in the "To:" field MAY be used for a reply message to all
recipients.
4.2.3 Cc
The "Cc:" field 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 additional recipients.
SEND RULES
Conforming implementations MAY send "Cc:" lists if all intended
recipients can be disclosed. The list of disclosed recipients MUST not
include those sent via a blind copy. If not, systems SHOULD omit the
"Cc:" fields or use the group notation from RFC822 to indicate that the
full list of recipients is unknown or otherwise unavailable.
Example:
Cc: +12145551213@mycompany.com
RECEIVE RULES
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Systems compliant to this profile SHOULD preserve these additional
recipients. On reception of a message, some systems MAY add all the
addresses in the "Cc:" field to the "To:" field, others MAY discard the
addresses in the "Cc:" fields. If a list of "Cc:" addresses is
present, these addresses MAY be used for a reply message to all
recipients.
4.2.4 Date
The "Date:" field MUST be present and contains the date, time, and time
zone in which the message was sent by the originator.
SEND RULES
The time zone MUST be present and 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 [RFC822] date and time stamps into local time.
If the VPIM sender is relaying a message from a system which does not
provide a time stamp, the time of arrival at the gateway system SHOULD
be used as the date.
Example:
Date: Wed, 28 Jul 96 10:08:49 -0800 (PST)
RECEIVE RULES
The sending system MUST report the time the message was sent. From
[RFC822]
4.2.5 Sender
SEND RULES
The "Sender:" 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 systems.
RECEPTION RULES
If the address in the "Sender:" field cannot be preserved in the
recipient's message queues or in the next-hop protocol from a gateway,
the field MAY be silently discarded.
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4.2.6 Return-Path
The "Return-path:" field 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. Note that if the
"Return-path:" is null ("<>"), e.g. no path, loop prevention or
confidential, delivery status and message disposition notifications MUST
NOT be sent.
RECEPTION RULES
If the receiving system is incapable of storing the return path to be
used for subsequent delivery errors, the receiving system must otherwise
ensure that further delivery errors don't happen. Systems that do not
support the return path MUST ensure that at the time the message is
acknowledged, the message is delivered to the recipient's ultimate
mailbox. Non-Delivery notifications should not be sent after that final
delivery.
4.2.7 Message-id
The "Message-Id:" field contains a unique per-message identifier.
SEND RULES
A unique message-id MUST be generated for each message sent from a VPIM-
compliant implementation.
Example:
Message-Id: <12345678@mycompany.com>
RECEPTION RULES
The message id is not required to be stored on the receiving system.
This identifier MAY be used for tracking, auditing, and returning
receipt notification reports. From [RFC822]
4.2.8 Reply-To
If present, the "Reply-to:" header provides a preferred address to which
reply messages should be sent (see 4.7.1). Typically, voice mail
systems can only support one originator of a message so it is likely
that this field will be ignored by the receiving system. From [RFC822]
SEND RULES
A compliant system SHOULD NOT send a Reply-To header.
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RECEPTION RULES
If a "reply-to:" field is present, a reply-to sender message MAY be
sent to the address specified (that is, in lieu of the address in the
"From:" field). If only one address of the originator is supported in
the message store or in the next-hop protocol from a multi-protocol
gateway, the address in the "From:" field MUST be used and the "Reply-
To:" field MAY be silently discarded.
4.2.9 Received
The "Received:" field contains trace information added to the beginning
of a RFC 822 message by MTAs. This is the only field 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. From
[RFC822]
SEND RULES
A VPIM-compliant system MUST add a "Received:" fields when acting as a
gateway.
RECEPTION RULES
A VPIM-compliant system SHOULD 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.
4.2.10 MIME Version
The "MIME-Version:" field indicates that the message conforms to [MIME].
Systems compliant with this specification SHOULD include a comment with
the words "(Voice 2.0)". [VPIM1] defines an earlier version of this
profile and uses the token (Voice 1.0). 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.
4.2.11 Content-Type
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. The allowable contents are detailed starting
in section 4.4 of this document. From [MIME2]
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4.2.12 Content-Transfer-Encoding
4.2.13 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". From [MIME1]Sensitivity
The "Sensitivity:" field, if present, indicates the requested privacy
level. The case-insensitive values "Personal", "Private", and "Normal"
are specified. If no privacy is requested, this field is omitted.
SEND RULES
A VPIM-compliant implementations MAY include this header to indicate the
sensitivity of a message. If the message is of "Normal" sensitivity,
this field MAY be omitted. From: [X.400]
RECEPTION RULES
If a "Sensitivity:" field with a value of "Personal" or "Private" is
present in the message, a compliant system SHOULD 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.
****** Authors Note: The following requirement from VPIM needs to be
evaluated in light of general Internet email client behaviors ******
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 (X.Y.Z)
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]
4.2.14 Importance
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 of the absent header assumed to be "normal". From: [X.400]
SEND RULES
Compliant implementations MAY include this header to indicate the
importance of a message
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RECEPTION RULES
If the receiving system does not support importance, the attribute may
be silently dropped. If the attribute is supported, it can be used for
various user interface purposes including the ordering messages within a
mailbox or trigging notification devices such as pagers.
4.2.15 Subject
The subject field is often provided by email systems but is not widely
supported on Voice Mail platforms. From [RFC822]
SEND RULES
For compatibility with text based mailbox interfaces, a text subject
field SHOULD be generated by a compliant implementation. 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 "Voice Message" for the benefit of GUI enabled
recipients.
RECEPTION RULES
It is anticipated that many voice-only systems will be incapable of
storing the subject line. The subject MAY be discarded if present by a
receiving system.
4.2.16 Disposition-Notification-To
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
SEND RULES
VPIM-compliant implementations MAY include this header to request a
disposition indication such as a listen confirmation.
RECEPTION RULES
The presence of a "Disposition-notification-to:" header in a message is
merely a request for an MDN described in 4.6.3. The recipients' system
is always free to silently ignore such a request so this header does not
burden any system that does not support it. From [MDN].
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4.2.17 Disposition-Notification-Options
This header MAY be present to define future extensions parameters for an
MDN requested by the presence of the header in the previous section.
SEND RULES
No "Disposition-notification-options:" are defined that are useful for
voice messaging. Sending systems SHOULD NOT request disposition
notification options by sending a disposition-notification-options
header.
RECEPTION RULES
Currently no parameters are defined by this document or by [MDN].
However for forward compatibility with future extensions,, this header
MUST be processed 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.
Example:
Disposition-notification-options:
whizzbang=required,foo
4.3 MIME Audio Content Descriptions
4.3.1 Content-Description:
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
4.3.2 Content-Disposition:
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/* 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]
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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(s) if
available to the originator
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).
4.3.3 Content-Duration:
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]
Example:
Content-Duration: 33
4.3.4 Content-Language:
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
4.4 Voice Message Content Types
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.
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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 not permitted If present, it MAY be tolerated, but some systems have
no means to tolerate other contents. In this case, the unsupported
content SHOULD be deleted and the remaining message delivered, however
systems MAY reject the entire message with 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.
4.4.1 Multipart/Voice-Message
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.
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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).
4.4.2 Message/RFC822
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 4.7) or to reply with original content
(see 4.7.1). From [MIME2]
RECEPTION RULES
The receiving system may flatten the forwarding structure if necessary.
If flattening, must discard other vCards of forwarded parts such that
only the outermost vCard is retained.
4.4.3 Text/Directory
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 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 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).
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The vCard profile [VCARD] 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. This address MAY be used for
reply-to-sender functionality when the RFC822 header
fields are not accessable to the voice mail helper
application.
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.
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.recipient media capabilities).
If present, the spoken name attribute MUST be denoted by a content ID
pointing to an audio/* content elsewhere in the VPIM message.
***** Authors Note: Some believe that this should be changed to "MUST
be included inline in the vCard". This change from RFC 2421 would
facilitate easier processing by desktop clients that launch vCard
viewers via helper application launched with only the contents of a
single mime body part. Comments are requested. ******
Each multipart/voice-message content MUST only contain one vCard -- more
than one is an error condition. A VPIM message may contain forwarded
messages. VCards that are part of the forwarded messages are permitted.
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 contained in message/rfc822
contents -- only the vCard of forwarding originator will be at the top-
level.
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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>
SOUND;TYPE=32KADPCM;ENCODING=B;
Base-64 encoded spoken name data ***** Alternative *****
REV:19960831T103310Z
Version: 3.0
END:VCARD
4.4.4 Audio/32KADPCM
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 0).
This encoding is a moderately compressed encoding with a data rate of 32
kbits/second using moderate processing resources.
4.4.5 Proprietary Voice or Fax Formats
Use of any other encoding except the required codecs reduces
interoperability in the absence of explicit knowledge about the
capabilities of the recipient. A compliant implementation MAY use any
other encoding 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. The fax encodings should be registered as sub-types
of Image.
SEND RULES
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Proprietary voice encoding formats or other standard formats MAY be sent
under this profile only if the sender has a reasonable expectation that
the recipient will accept the encoding. In practice, this requires
explicit per-destination configuration information maintained either in
a directory, personal address book, or gateway configuration tables.
RECEIVE RULES
Systems which receive audio/* or image/* content types which they are
unable to decode MUST return the message to the originator with an NDN
indicating media not supported.
4.5 Other MIME Content Types
Only the above-specified contents are required to be supported within a
multipart/voice message by a receiving system. Other contents MUST NOT
be included within the multipart/voice-message.
An implementation compliant with this profile MAY send additional
contents in a VPIM message, but only outside the multipart/voice-
message. 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 multipart/voice-message
content type) with any of the contents defined in 4.34.3 & Error!
Reference source not found.Error! Reference source not found., 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 within a
multipart/voice message (with other noted contents below them as
required.) 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.
4.5.1 Image/Tiff
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 within 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.
SEND RULES
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All VPIM implementations that support facsimile MUST 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.
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).
RECEIVE RULES
A receiving system MAY accept the voice content of a VPIM message and
discard the fax content. The recipient MAY be notified of the dropped
content. Though discouraged, a recipient system MAY reject (with
appropriate NDN) the entire message if it cannot handle fax
attachements.
4.5.2 Multipart/Mixed
Multipart/mixed contents MAY be sent as the top level of a VPIM message.
Typically, this would only be used when attaching non-voice or fax
content to a VPIM message. These other contents SHOULD be placed after
the multipart/voice-message.
SEND RULES
Multipart/mixed provides the facilities for enclosing several body parts
in a single message. When used in a VPIM message, multipart/mixed is the
top level content type and multipart/voice-message is the first second
level content type. Other attachments follow as additioanl second level
content types. Multipart/mixed may also be used within a
multipart/voice-message but its use is undefined. Note that the
semantics of using complex hierarchy within a voice message is undefined
and the use of such a structure is discouraged.
RECEIVE RULES
Compliant systems MUST accept multipart/mixed content types both at the
top level and within a multipart/voice-messages. Systems may collapse
the contents of the multipart/mixed structure into the multipart/voice
message itself. If necessary, systems SHOULD discard the other contents
to deliver the voice content but they MAY reject the entire message if
this is not possible. From [MIME2]
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4.5.3 Text/Plain
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.
SEND RULES
Compliant VPIM implementations SHOULD NOT send the Text/Plain content-
type. It should be understood that the textual information is not
considered a primary media within multipart/voice-message and may be
discarded (or rejected) by a receiving system.
RECEIVE RULES
Within a multipart/voice message, the text/plain content type MAY be
dropped from the message. The recipient SHOULD NOT reject the entire
message (if an implementation does reject the entire message a suitable
DSN MUST be used).
Outside a Multipart/Voice-message, 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 and no
indication of its presence can be given to the recipient, the entire
message MUST be returned to the sender with a negative delivery status
notification and a media-unsupported status code.
4.6 Return and Notification Messages
VPIM delivery status notification messages (4.6.2) 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 (4.6.3) should be sent to the sender
specified in the Disposition-Notification-To header field (4.2.16). The
MDN should be sent 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).
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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 (4.6.1)
and SHOULD contain a spoken error message.
4.6.1 Multipart/Report
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 MAY include the
human-readable description of the error as a spoken audio/* content
(this speech MAY 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.
4.6.2 Message/Delivery-status
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]
4.6.3 Message/Disposition-notification
This MIME body part is used for sending machine-parsable read-receipt
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 0. Conforming implementations should recognize and decode the
Message/Disposition-notification content type and present the
notification to the user. From [MDN]
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4.7 Forwarded Messages
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.
4.7.1 Message/RFC822
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 4.7) or to reply with original content
(see 4.7.1). From [MIME2]
RECEPTION RULES
May flatten structure if necessary to fit within the message structure
of the recipients voice mailbox.
4.8 Reply Messages
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. It is expected that within legacy email
implementations, the voice message viewer application may need to create
a reply message without the benefit of the RFC822 headers. In such a
case, the vCard MAY be used to generate a reply to the sender.
RECEPTION RULES
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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.
4.9 Notification Messages
VPIM delivery status notification messages (4.6.2) 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 (4.6.3) 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 (4.6.1)
and SHOULD contain a spoken error message.
If a VPIM system receives a message with contents that are not
understood (see 4.3 & Error! Reference source not found.), 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.
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5. Message Transport Protocol
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 "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.
5.1 ESMTP Commands
5.1.1 HELO
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]
5.1.2 MAIL FROM (REQUIRED)
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]
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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 message).
From [SMTP]
5.1.3 RCPT TO
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.
5.1.4 DATA
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]
5.1.5 TURN
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]
5.1.6 QUIT
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]
5.1.7 RSET
Resets the connection to its initial state. Compliant implementations
MUST implement the RSET command. From [SMTP]
5.1.8 VRFY
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]
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(Note that the implementation of VRFY may simplify the guessing of a
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]
5.1.9 EHLO
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]
5.1.10 BDAT
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]
5.2 ESMTP Keywords
The following ESMTP keywords indicate extended features useful for voice
messaging.
5.2.1 PIPELINING
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]
5.2.2 SIZE
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]
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5.2.3 CHUNKING
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]
5.2.4 BINARYMIME
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]
5.2.5 DSN
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].
5.2.6 ENHANCEDSTATUSCODES
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
notification format defined in [DSN]. Compliant implementations SHOULD
support this capability. From [STATUS]
5.3 ESMTP Parameters - MAIL FROM
5.3.1 BINARYMIME
The current message is a binary encoded MIME messages. Compliant
implementations SHOULD support binary transport indicated by this
parameter. From [BINARY]
5.3.2 RET
The RET parameter indicates whether the content of the message should be
returned. Compliant systems SHOULD honor a request for returned
content. From [DRPT]
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5.3.3 ENVID
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]
5.4 ESMTP Parameters - RCPT TO
5.4.1 NOTIFY
The NOTIFY parameter indicates the conditions under which a delivery
report should be sent. Compliant implementations MUST honor this
request. From [DRPT]
5.4.2 ORCPT
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]
5.5 ESMTP - SMTP Downgrading
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 is 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 notification
to the originator, e.g. the message left an ESMTP host and was sent
(unreliably) via SMTP.
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6. Directory Address Resolution
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.
7. Management Protocols
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.
7.1 Network Management
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]
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8. Conformance Requirements
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.
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.
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9. Security Considerations
9.1 General Directive
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 Internet security infrastructure, rather
than a new mechanism or some other mechanism outside of the Internet
infrastructure.
9.2 Threats and Problems
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 that ensue from integrating the two services.
9.2.1 Spoofed sender
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 sender's 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.
9.2.2 Unsolicited voice mail
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 curb this problem.
9.2.3 Message disclosure
Users of voice messaging systems have an expectation of a level of
message privacy that 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.
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9.3 Security Techniques
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.
10. References
[8BIT] Klensin, J., Freed, N., Rose, M., Stefferud, E., D. Crocker, "SMTP
Service Extension for 8bit-MIMEtransport" RFC 1426, United Nations
University, Innosoft International, Inc., Dover Beach Consulting, Inc.,
Network Management Associates, Inc., The Branch Office, February 1993.
[ADPCM] G. Vaudreuil 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,
01/15/1996.
[MIMEDIR] F. Dawson, T. Howes, & M. Smith, "A MIME Content-Type for
Directory Information", RFC 2425 September 1998
[DISP] R. Troost 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",
RFC1035, Nov 1987.
[DNS2] Mockapetris, P., "Domain names - concepts and facilities", RFC 1034,
Nov 1987.
[DRPT] Moore, K. "SMTP Service Extensions for Delivery Status
Notifications", RFC 1891, 01/15/1996
[DSN] Moore, K., Vaudreuil, G., "An Extensible Message Format for Delivery
Status Notifications", RFC 1894, 01/15/1996.
[DUR] G. Parsons and G. Vaudreuil, "Content Duration MIME Header
Definition", RFC 2424, September 1998.
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[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, United Nations University, Innosoft
International, Inc., Dover Beach Consulting, Inc., Network Management
Associates, Inc., The Branch Office, 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,
Mar 1995
[MDN] Fajman, Roger, "An Extensible Message Format for Message Disposition
Notifications" RFC 2298, March 1998
[MIB II] M. Rose, "Management Information Base for Network Management of
TCP/IP-based internets: MIB-II", RFC 1158, May 1990.
[MIME1] N. Freed and N. Borenstein, "Multipurpose Internet Mail Extensions
(MIME) Part One: Format of Internet Message Bodies", RFC 2045,
Innosoft, First Virtual, Nov 1996.
[MIME2] N. Freed and N. Borenstein, "Multipurpose Internet Mail Extensions
(MIME) Part Two: Media Types ", RFC 2046, Innosoft, First Virtual, Nov
1996.
[MIME3] K. Moore, "Multipurpose Internet Mail Extensions (MIME) Part
Three: Message Header Extensions for Non-ASCII Text ", RFC 2047,
University of Tennessee, Nov 1996.
[MIME4] N. Freed, J. Klensin and J. Postel, "Multipurpose Internet Mail
Extensions (MIME) Part Four: Registration Procedures", RFC 2048,
Innosoft, MCI, ISI, Nov 1996.
[MIME5] N. Freed and N. Borenstein, "Multipurpose Internet Mail Extensions
(MIME) Part Five: Conformance Criteria and Examples ", RFC 2049,
Innosoft, First Virtual, Nov 1996.
[PIPE] Freed, N., Cargille, A., "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,
01/15/1996.
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[REQ] S. Bradner, "Key words for use in RFCs to Indicate Requirement
Levels", RFC 2119, March 1997.
[RFC822] Crocker, D., "Standard for the Format of ARPA Internet Text
Messages", STD 11, RFC 822, UDEL, August 1982.
[SIZE] Klensin, J, Freed, N., Moore, K, "SMTP Service Extensions for
Message Size Declaration" RFC 1870, United Nations University,
Innosoft International, Inc., November 1995.
[SMTP] Postel, J., "Simple Mail Transfer Protocol", STD 10, RFC 821,
USC/Information Sciences Institute, August 1982.
[STATUS] Freed, N. "SMTP Service Extension for Returning Enhanced Error
Codes", RFC 2034, 10/30/1996.
[TIFF-F] G. Parsons and J. Rafferty, "Tag Image File Format: Application
F", RFC 2306 , March 1998.
[TIFFREG] G. Parsons, J. Rafferty & S. Zilles, "Tag Image File Format:
image/tiff - MIME sub-type registraion", RFC 2302, March 1998.
[V-MSG] G. Vaudreuil and G. Parsons, "VPIM Voice Message: MIME Sub-type
Registration", RFC 2022, September 1998.
[VCARD] Dawson, Frank, Howes, Tim, "vCard MIME Directory Profile" RFC 2426,
September 1998.
[VPIM1] Vaudreuil, Greg, "Voice Profile for Internet Mail", RFC 1911, Feb
1996.
[VPIM2] Vaudreuil, Greg, Parsons, Glen, "Voice Profile for Internet Mail,
Version 2", RFC 2421, September 1998.
[X.400] Hardcastle-Kille, S., "Mapping between X.400(1988) / ISO 10021 and
RFC 822", RFC 1327, May 1992.
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11. Acknowledgments
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.
12. Copyright Notice
"Copyright (C) The Internet Society (1999). 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."
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13. Authors' Addresses
Glenn W. Parsons
Nortel Networks
P.O. Box 3511, Station C
Ottawa, ON K1Y 4H7
Canada
Phone: +1-613-763-7582
Fax: +1-613-763-4461
Glenn.Parsons@NortelNetworks.com
Gregory M. Vaudreuil
Lucent Technologies
7291 Williamson Rd
Dallas, TX 75214
United States
Phone/Fax: +1-972-733-2722
GregV@Lucent.Com
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14. Appendix A - VPIM Requirements Summary
The following table summarizes the profile of VPIM version 2 detailed in
this document. Since in many cases it is not possible to simplify the
qualifications for supporting each feature this appendix is informative.
The reader is recommended to read the complete explanation of each
feature in the referenced section. The text in the previous sections
shall be deemed authoritative if any item in this table is ambiguous.
The conformance table is separated into various columns:
Feature - name of protocol feature (note that the indenting
indicates a hierarchy of conformance, i.e. the
conformance of a lower feature is only relevant if there
is conformance to the higher feature)
Section - reference section in main text of this document
Area - conformance area to which each feature applies:
C - content
T - transport
Status - whether the feature is mandatory, optional, or prohibited.
The key words used in this table are to be interpreted as described in
[REQ], though the following list gives a quick overview of the
different degrees of feature conformance:
Must - mandatory
Should - required in the absence of a compelling
need to omit.
May - optional
Should not - prohibited in the absence of a compelling
need.
Must not - prohibited
Footnote - special comment about conformance for a particular feature
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VPIM version 2 Conformance
| | | | |S| |
| | | | | |H| |F
| | | | | |O|M|o
| | | |S| |U|U|o
| | | |H| |L|S|t
| |A|M|O| |D|T|n
| |R|U|U|M| | |o
| |E|S|L|A|N|N|t
| |A|T|D|Y|O|O|t
FEATURE |SECTION | | | | |T|T|e
-------------------------------------------|----------|-|-|-|-|-|-|-
| | | | | | | |
Message Addressing Formats: | | | | | | | |
Use DNS host names |4.1 |C|x| | | | |
Use only numbers in mailbox IDs |4.1.1 |C| |x| | | |
Use alpha-numeric mailbox IDs |4.1.1 |C| | |x| | |
Support of postmaster@domain |4.1.2 |C|x| | | | |
Support of non-mail-user@domain |4.1.2 |C| |x| | | |
Support of distribution lists |4.1.3 |C| |x| | | |
| | | | | | | |
Message Header Fields: | | | | | | | |
Encoding outbound messages | | | | | | | |
From |4.2.1 |C|x| | | | |
Addition of text name |4.2.1 |C| |x| | | |
To |4.2.2 |C| |x| | | |1
cc |4.2.3 |C| |x| | | |1
Date |4.2.4 |C|x| | | | |
Sender |4.2.5 |C| | |x| | |
Return-Path |4.2.6 |C| | | |x| |
Message-id |4.2.7 |C|x| | | | |
Reply-To |4.2.8 |C| | | |x| |
Received |0 |C|x| | | | |
MIME Version: 1.0 (Voice 2.0) |4.2.10 |C| |x| | | |
Content-Type |4.2.11 |C|x| | | | |
Content-Transfer-Encoding |4.2.12 |C|x| | | | |
Sensitivity |4.2.13 |C| | |x| | |
Importance |4.2.14 |C| | |x| | |
Subject |0 |C| |x| | | |
Disposition-notification-to |0 |C| | |x| | |
Disposition-notification-options |4.2.17 |C| | |x| | |
Other Headers |4.2 |C| | |x| | |
| | | | | | | |
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| | | | |S| |
| | | | | |H| |F
| | | | | |O|M|o
| | | |S| |U|U|o
| | | |H| |L|S|t
| |A|M|O| |D|T|n
| |R|U|U|M| | |o
| |E|S|L|A|N|N|t
| |A|T|D|Y|O|O|t
FEATURE |SECTION | | | | |T|T|e
-------------------------------------------|----------|-|-|-|-|-|-|-
Detection & Decoding inbound messages | | | | | | | |
From |4.2.1 |C|x| | | | |
Present text personal name |4.2.1 |C| | |x| | |
To |4.2.2 |C|x| | | | |
cc |4.2.3 |C| | |x| | |
Date |4.2.4 |C|x| | | | |
Conversion of Date to local time |4.2.4 |C| |x| | | |
Sender |4.2.5 |C| | |x| | |
Return-Path |4.2.6 |C| |x| | | |
Message ID |4.2.7 |C|x| | | | |
Reply-To |4.2.8 |C| | |x| | |
Received |4.2.9 |C| | |x| | |
MIME Version: 1.0 (Voice 2.0) |4.2.10 |C| |x| | | |
Content Type |4.2.11 |C|x| | | | |
Content-Transfer-Encoding |4.2.12 |C|x| | | | |
Sensitivity |4.2.13 |C|x| | | | |2
Importance |4.2.14 |C| | |x| | |
Subject |0 |C| | |x| | |
Disposition-notification-to |0 |C| | |x| | |
Disposition-notification-options |4.2.17 |C| | |x| | |
Other Headers |4.2 |C|x| | | | |3
| | | | | | | |
Message Content Encoding: | | | | | | | |
Encoding outbound audio/fax contents | | | | | | | |
7BIT |4.3 |C| | | | |x|
8BIT |4.3 |C| | | | |x|
Quoted Printable |4.3 |C| | | | |x|
Base64 |4.3 |C|x| | | | |4
Binary |4.3 |C| |x| | | |5
Detection & decoding inbound messages | | | | | | | |
7BIT |4.3 |C|x| | | | |
8BIT |4.3 |C|x| | | | |
Quoted Printable |4.3 |C|x| | | | |
Base64 |4.3 |C|x| | | | |
Binary |4.3 |C|x| | | | |5
| | | | | | | |
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