Internet Engineering Task Force (IETF) A. Melnikov, Ed.
Request for Comments: 6047 Isode Ltd
Obsoletes: 2447 December 2010
Category: Standards Track
ISSN: 2070-1721
iCalendar Message-Based Interoperability Protocol (iMIP)
Abstract
This document, "iCalendar Message-Based Interoperability Protocol
(iMIP)", specifies a binding from the iCalendar Transport-independent
Interoperability Protocol (iTIP) to Internet email-based transports.
Calendaring entries defined by the iCalendar Object Model (iCalendar)
are wrapped using constructs from RFC 5322 and MIME (RFC 2045, RFC
2046, RFC 2047, and RFC 2049), and then transported over SMTP.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc6047.
Copyright Notice
Copyright (c) 2010 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Melnikov Standards Track [Page 1]RFC 6047 iMIP December 2010
This document may contain material from IETF Documents or IETF
Contributions published or made publicly available before November
10, 2008. The person(s) controlling the copyright in some of this
material may not have granted the IETF Trust the right to allow
modifications of such material outside the IETF Standards Process.
Without obtaining an adequate license from the person(s) controlling
the copyright in such materials, this document may not be modified
outside the IETF Standards Process, and derivative works of it may
not be created outside the IETF Standards Process, except to format
it for publication as an RFC or to translate it into languages other
than English.
Table of Contents
1. Introduction ....................................................3
1.1. Related Memos ..............................................3
1.2. Formatting Conventions .....................................3
1.3. Terminology ................................................4
2. MIME Message Format Binding .....................................4
2.1. MIME Media Type ............................................4
2.2. Security ...................................................5
2.2.1. Authorization .......................................5
2.2.2. Authentication ......................................5
2.2.3. Confidentiality .....................................5
2.3. Email Addresses ............................................6
2.4. Content-Type Header Field ..................................6
2.5. Content-Transfer-Encoding Header Field .....................7
2.6. Content-Disposition Header Field ...........................8
3. Security Considerations .........................................8
4. Examples .......................................................11
4.1. Single Component with an ATTACH Property ..................11
4.2. Using multipart/alternative for Low-Fidelity Clients ......11
4.3. Single Component with an ATTACH Property and
Inline Attachment .........................................12
4.4. Multiple Similar Components ...............................14
4.5. Multiple Mixed Components .................................15
4.6. Detailed Components with an ATTACH Property ...............16
5. Recommended Practices ..........................................18
5.1. Use of Content and Message IDs ............................18
6. IANA Considerations ............................................18
7. References .....................................................19
7.1. Normative References ......................................19
7.2. Informative References ....................................20
Appendix A. Changes since RFC 2447 ................................21
Appendix B. Acknowledgements ......................................22
Melnikov Standards Track [Page 2]RFC 6047 iMIP December 2010
1. Introduction
This document provides the transport-specific information ("binding")
necessary to convey iCalendar Transport-independent Interoperability
Protocol (iTIP) [iTIP] over Internet email (using MIME) as defined in
[RFC5322] and [RFC2045]. Therefore, this document defines the
iCalendar Message-Based Interoperability Protocol (iMIP).
1.1. Related Memos
Implementers will need to be familiar with several other memos that,
along with this memo, form a framework for Internet calendaring and
scheduling standards.
This document specifies an Internet email binding for iTIP.
[iCAL] specifies a core specification of objects, data types,
properties, and property parameters.
[iTIP] specifies an interoperability protocol for scheduling between
different implementations.
This memo does not attempt to repeat the specification of concepts or
definitions from these other memos. Where possible, references are
made to the memo that provides for the specification of these
concepts or definitions.
1.2. Formatting Conventions
The mechanisms defined in this memo are defined in prose. In order
to refer to elements of the calendaring and scheduling model, core
object, or interoperability protocol defined in [iCAL] and [iTIP],
some formatting conventions have been used.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
Calendaring and scheduling roles are referred to in quoted strings of
text with the first character of each word in uppercase. For
example, "Organizer" refers to a role of a "Calendar User" within the
scheduling protocol defined by [iTIP].
Calendar components defined by [iCAL] are referred to with
capitalized, quoted strings of text. All calendar components start
with the letter "V". For example, "VEVENT" refers to the event
calendar component, "VTODO" refers to the to-do calendar component,
and "VJOURNAL" refers to the daily journal calendar component.
Melnikov Standards Track [Page 3]RFC 6047 iMIP December 2010
Scheduling methods defined by [iTIP] are referred to with
capitalized, quoted strings of text. For example, "REQUEST" refers
to the method for requesting a scheduling calendar component be
created or modified; "REPLY" refers to the method a recipient of a
request uses to update their status with the "Organizer" of the
calendar component.
Properties defined by [iCAL] are referred to with capitalized, quoted
strings of text, followed by the word "property". For example,
"ATTENDEE" property refers to the iCalendar property used to convey
the calendar address of a "Calendar User".
Property parameters defined by [iCAL] are referred to with lowercase,
quoted strings of text, followed by the word "parameter". For
example, "value" parameter refers to the iCalendar property parameter
used to override the default data type for a property value.
1.3. Terminology
The email terms used in this memo are defined in [RFC5322] and
[RFC2045]. The calendaring and scheduling terms used in this memo
are defined in [iCAL] and [iTIP].
2. MIME Message Format Binding
This section defines the message binding to the MIME electronic mail
transport.
The sections below refer to the "originator" and the "recipient" of
an iMIP message. In the case of a "request" method, the originator
is the "Organizer" and the recipient is an "Attendee" of the event.
In the case of a "response" method, the originator is an "Attendee"
and the recipient is the "Organizer" of the event.
The [RFC5322] "Reply-To" header field typically contains the email
address of the originator of the scheduling message. However, this
cannot be guaranteed because the sender of the iMIP message might not
be the originator of the scheduling message and the sender's "Mail
User Agent" (MUA) might not enforce iMIP semantics by translating the
originator's address into the "Reply-To" email header field.
2.1. MIME Media Type
A MIME entity containing content information formatted according to
this document will be referenced as a "text/calendar" content type
[iCAL]. It is assumed that this content type will be transported
through a MIME electronic mail transport.
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2.2. Security
This section addresses several aspects of security including
authentication, authorization, and confidentiality. Authentication
and confidentiality can be achieved using Secure/MIME (S/MIME)
[RFC5750] [RFC5751], which uses the Security Multiparts framework for
MIME [RFC1847].
2.2.1. Authorization
In iTIP messages [iTIP], only the "Organizer" is authorized to modify
or cancel calendar entries she organizes. That is,
spoof@xyz.example.net is not allowed to modify or cancel a meeting
that was organized by a@example.com. Furthermore, only the
respondent has the authorization to indicate their status to the
"Organizer". That is, the "Organizer" MUST ignore an iTIP message
from spoof@xyz.example.net that declines a meeting invitation for
b@example.com.
Implementations of iMIP SHOULD verify the authenticity of the creator
of an iCalendar object before taking any action. Methods for doing
this are presented later in this document.
[RFC1847] message flow in iTIP supports someone working on behalf of
a "Calendar User" through use of the "sent-by" parameter that is
associated with the "ATTENDEE" and "ORGANIZER" properties. However,
there is no mechanism to verify whether or not a "Calendar User" has
authorized someone to work on their behalf. It is left to
implementations to provide mechanisms for the "Calendar Users" to
make that decision.
2.2.2. Authentication
Authentication MUST be performed using S/MIME [RFC5750] [RFC5751].
Authentication is possible only on messages that have been signed.
Unauthenticated messages (i.e., unsigned messages) may not be
trusted.
2.2.3. Confidentiality
To ensure confidentiality using iMIP, implementations SHOULD utilize
encryption specified in S/MIME [RFC5750] [RFC5751]. iMIP does not
restrict a "Calendar User Agent" (CUA) from forwarding iCalendar
objects to other users or agents.
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2.3. Email Addresses
The calendar address specified within the "ORGANIZER" and "ATTENDEE"
properties in an iCalendar object sent using iMIP MUST be a proper
"mailto:" [MAILTO] URI specification for the corresponding
"Organizer" or "Attendee" of the "VEVENT" or "VTODO".
Because [iTIP] does not preclude "Attendees" from forwarding
"VEVENT"s or "VTODO"s to others, the [RFC5322] "Sender" value may not
equal that of the "Organizer". Additionally, the "Organizer" or
"Attendee" cannot be reliably inferred by the [RFC5322] "Sender" or
"Reply-To" header field values of an iMIP message. The relevant
address MUST be ascertained by opening the "text/calendar" MIME body
part and examining the "ATTENDEE" and "ORGANIZER" properties.
2.4. Content-Type Header Field
A MIME body part containing content information that conforms to this
document MUST have an [RFC2045] "Content-Type" value of
"text/calendar". The [RFC2045] "Content-Type" header field MUST also
include the MIME parameter "method". The value MUST be the same
(ignoring case) as the value of the "METHOD" property within the
iCalendar object.
Note 1: A MIME message containing multiple iCalendar objects with
different "method" values MUST be further encapsulated with a
"multipart/mixed" MIME entity [RFC2046]. This will allow each of
the iCalendar objects to be encapsulated within their own
"text/calendar" MIME entity.
Note 2: A MIME body part with a "Content-Type" value of
"text/calendar" that lacks the "method" parameter is not
considered to be an iMIP body part and thus is not subject to the
requirements specified in this document.
Note that according to [iCAL] the default character set for iCalendar
objects is UTF-8 [UTF-8]. However, the default character set for a
"text/*" MIME entity according to [RFC2046] is US-ASCII. Thus, a
"charset" MIME parameter MUST be present if the iCalendar object
contains characters that can't be represented in the US-ASCII
character set and, as specified in [iCAL], it MUST have the value
"UTF-8".
The optional "component" MIME parameter defines the iCalendar
component type contained within the iCalendar object.
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The following is an example of this header field with a value that
indicates an event message.
Content-Type: text/calendar; method=REQUEST; charset=UTF-8;
component=vevent
The "text/calendar" content type allows for the scheduling message
type to be included in a MIME message with other content information
(i.e., "multipart/mixed") or included in a MIME message with a clear-
text, human-readable form of the scheduling message (i.e.,
"multipart/alternative" [RFC2046]).
In order to permit the information in the scheduling message to be
understood by MIME User Agents (UAs) that do not support the
"text/calendar" content type, scheduling messages SHOULD be sent with
an alternative, human-readable form of the information.
Note that "multipart/alternative" MUST NOT be used to represent two
slightly different iCalendar objects, for example, two "VEVENT"s with
alternative starting times.
CUAs can use other MIME parameters of the "Content-Type" header
field, as well as a language specified in the Content-Language header
field [RFC3282], to pick a "text/calendar" part for processing if a
"multipart/alternative" MIME message contains more than one
"text/calendar" part.
Any receiving UA compliant with this specification MUST be able to
process "text/calendar" body parts enclosed within "multipart/*".
Note that a "multipart/mixed" MIME message can include multiple
"text/calendar" components. The receiving UA MUST be able to process
all of them.
2.5. Content-Transfer-Encoding Header Field
Unless an iMIP message is transported over 8-bit clean transport
(such as SMTP [8BITMIME]), a transfer encoding such as quoted-
printable or base64 [RFC2045] MUST be used for iCalendar objects
containing any characters that can't be represented in the US-ASCII
character set. For example:
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From: user1@example.com
To: user2@example.com
Subject: Phone Conference
Mime-Version: 1.0
Date: Wed, 07 May 2008 21:30:25 +0400
Message-ID: <4821E731.5040506@laptop1.example.com>
Content-Type: text/calendar; method=REQUEST; charset=UTF-8
Content-Transfer-Encoding: quoted-printable
BEGIN:VCALENDAR
PRODID:-//Example/ExampleCalendarClient//EN
METHOD:REQUEST
VERSION:2.0
BEGIN:VEVENT
ORGANIZER:mailto:user1@example.com
ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:mailto:user1@example.com
ATTENDEE;RSVP=YES;CUTYPE=INDIVIDUAL:mailto:user2@example.com
DTSTAMP:20080507T170000Z
DTSTART:20080701T160000Z
DTEND:20080701T163000Z
SUMMARY:Phone call to discuss your last visit
DESCRIPTION:=D1=82=D1=8B =D0=BA=D0=B0=D0=BA - =D0=B4=D0=BE=D0=
=B2=D0=BE=D0=BB=D0=B5=D0=BD =D0=BF=D0=BE=D0=B5=D0=B7=D0=B4=D0=BA=D0
=BE=D0=B9?
UID:calsvr.example.com-8739701987387998
SEQUENCE:0
STATUS:TENTATIVE
END:VEVENT
END:VCALENDAR
2.6. Content-Disposition Header Field
Implementations MAY include a "Content-Disposition" header field to
define a file name for an iCalendar object. However, the handling of
a MIME part MUST be based on its [RFC2045] "Content-Type" and not on
the extension specified in the "Content-Disposition", as different
email malware is known to trick User Agents into misinterpreting
content of messages by specifying a file extension in the Content-
Disposition header field that doesn't correspond to the value of the
"Content-Type" header field.
3. Security Considerations
The security threats that applications must address when implementing
iTIP are detailed in [iTIP]. In particular, two spoofing threats are
identified in Section 6.1 of [iTIP]: spoofing the "Organizer", and
spoofing an "Attendee". To address these threats, the originator of
an iCalendar object must be authenticated by a recipient. Once
Melnikov Standards Track [Page 8]RFC 6047 iMIP December 2010
authenticated, a determination can be made as to whether or not the
originator is authorized to perform the requested operation.
Compliant applications MUST support signing and encrypting
"text/calendar" body parts using a mechanism based on S/MIME
[RFC5750] [RFC5751] in order to facilitate the authentication of the
originator of the iCalendar object (see Sections 2.2.2 and 2.2.3).
The steps for processing a signed iMIP message are described below:
1. Using S/MIME, determine who signed the "text/calendar" body part
containing the iCalendar object. This is the "signer". (Note
that the email address of the signer MUST be specified in the
rfc822Name field of the "subject alternative name" extension of
the signer certificate, as specified in [RFC5280],
Section 4.1.2.6.) Note that the signer is not necessarily the
person sending an e-mail message, since an e-mail message can be
forwarded.
2. Correlate the signer to either an "ATTENDEE" property or to the
"ORGANIZER" property in the iCalendar object, based on the method
and the calendar component specified in the iCalendar object, as
defined in Section 1.4 of [iTIP]. If the signer cannot be
correlated to an "ATTENDEE"/"ORGANIZER" property, then actively
warn the user controlling the "Calendar User Agent" that the
iCalendar object is untrusted, and encourage the user to ignore
the message, but give advanced users the option to (a) view the
certificate of the signer and the entire certificate chain (if
any) in order to help decide if the signer should be trusted to
send the message, and then (b) allow the CUA to accept and process
the iCalendar object.
3. Determine whether or not the "ATTENDEE"/"ORGANIZER" is authorized
to perform the operation as defined by [iTIP]. If the conditions
are not met, ignore the message.
4. If all the above conditions are met, the message can be processed.
S/MIME signing also protects against malicious changes to messages in
transit.
If calendar confidentiality is required by the sender, signed iMIP
messages SHOULD be encrypted by a mechanism based on S/MIME [RFC5750]
[RFC5751]. If iMIP is used within a single ADministrative Management
Domain (ADMD) [RFC5598], SMTP STARTTLS [SMTP-TLS] (together with
STARTTLS in IMAP/POP [IMAP-POP-TLS]) MAY alternatively be used to
provide calendar confidentiality.
Melnikov Standards Track [Page 9]RFC 6047 iMIP December 2010
Once a signed and/or encrypted iMIP message is received and
successfully verified (as detailed above) by a CUA, the CUA SHOULD
remember whether the sender of the message is using signing and/or
encrypting. If an unsigned iMIP message is received from the same
sender later on, the receiving CUA SHOULD warn the receiving user
about a possible man-in-the-middle attack and SHOULD ignore the
message, unless explicitly overridden by the user.
Implementations MAY provide means for users to disable signing and
encrypting.
It is possible to receive iMIP messages sent by someone working on
behalf of another "Calendar User". This is determined by examining
the "sent-by" parameter in the relevant "ORGANIZER" or "ATTENDEE"
property. [iCAL] and [iTIP] provide no mechanism to verify that a
"Calendar User" has authorized someone else to work on their behalf.
To address this security issue, implementations MUST provide
mechanisms for the "Calendar Users" to make that decision before
applying changes from someone working on behalf of a "Calendar User".
One way to achieve this is to reject iMIP messages sent by users
other than the "ORGANIZER" or the "ATTENDEE"s. Alternatively, the
receiver could have a list of trusted <sent-by, organizer> proxies in
its local security policy. And yet another way is to prompt the user
for confirmation.
iMIP-based calendaring is frequently deployed within a single ADMD,
with boundary filtering employed to restrict email calendaring flows
to be inside the ADMD. This can help in minimizing malicious changes
to calendaring messages in transit, as well as in making
authorization decisions less risky.
A security consideration associated with the use of the Content-
Disposition header field is described in Section 2.6.
Use of S/MIME makes the security considerations discussed in
[RFC5750] [RFC5751] relevant to this document. For additional
security considerations regarding certificate and Certificate
Revocation List (CRL) verification, please see [RFC5280].
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4. Examples
4.1. Single Component with an ATTACH Property
This minimal message shows how an iCalendar object references an
attachment. The attachment is accessible via its URL.
From: sman@netscape.example.com
To: stevesil@microsoft.example.com
Subject: Phone Conference
Mime-Version: 1.0
Content-Type: text/calendar; method=REQUEST; charset=US-ASCII
Content-Transfer-Encoding: 7bit
BEGIN:VCALENDAR
PRODID:-//Example/ExampleCalendarClient//EN
METHOD:REQUEST
VERSION:2.0
BEGIN:VEVENT
ORGANIZER:mailto:man@netscape.example.com
ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:mailto:man@netscape.example.com
ATTENDEE;RSVP=YES:mailto:stevesil@microsoft.example.com
DTSTAMP:19970611T190000Z
DTSTART:19970701T210000Z
DTEND:19970701T230000Z
SUMMARY:Phone Conference
DESCRIPTION:Please review the attached document.
UID:calsvr.example.com-873970198738777
ATTACH:ftp://ftp.bar.example.com/pub/docs/foo.doc
STATUS:CONFIRMED
END:VEVENT
END:VCALENDAR
4.2. Using multipart/alternative for Low-Fidelity Clients
This example shows how a client can emit a multipart message that
includes both a plain text version and the full iCalendar object.
Clients that do not support "text/calendar" will still be capable of
rendering the plain text representation.
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From: foo1@example.com
To: foo2@example.com
Subject: Phone Conference
Mime-Version: 1.0
Content-Type: multipart/alternative; boundary="01BD3665.3AF0D360"
--01BD3665.3AF0D360
Content-Type: text/plain; charset=us-ascii
Content-Transfer-Encoding: 7bit
This is an alternative representation of a "text/calendar"
MIME object.
When: 7/1/1997 10:00AM PDT - 7/1/97 10:30AM PDT
Where:
Organizer: foo1@example.com
Summary: Phone Conference
--01BD3665.3AF0D360
Content-Type: text/calendar; method=REQUEST; charset=US-ASCII
Content-Transfer-Encoding: 7bit
BEGIN:VCALENDAR
PRODID:-//Example/ExampleCalendarClient//EN
METHOD:REQUEST
VERSION:2.0
BEGIN:VEVENT
ORGANIZER:mailto:foo1@example.com
ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:mailto:foo1@example.com
ATTENDEE;RSVP=YES;CUTYPE=INDIVIDUAL:mailto:foo2@example.com
DTSTAMP:19970611T190000Z
DTSTART:19970701T170000Z
DTEND:19970701T173000Z
SUMMARY:Phone Conference
UID:calsvr.example.com-8739701987387771
SEQUENCE:0
STATUS:CONFIRMED
END:VEVENT
END:VCALENDAR
--01BD3665.3AF0D360
4.3. Single Component with an ATTACH Property and Inline Attachment
This example shows how a message containing an iCalendar object
references an attached document. The reference is made using a
Content-ID (CID). Thus, the iCalendar object and the document are
packaged in a "multipart/related" encapsulation.
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RFC 6047 iMIP December 2010
From: foo1@example.com
To: foo2@example.com
Subject: Phone Conference
Mime-Version: 1.0
Content-Type: multipart/related; boundary="boundary-example-1"
--boundary-example-1
Content-Type: text/calendar; method=REQUEST; charset=US-ASCII
Content-Transfer-Encoding: 7bit
Content-Disposition: attachment; filename="event.ics"
BEGIN:VCALENDAR
PRODID:-//Example/ExampleCalendarClient//EN
METHOD:REQUEST
VERSION:2.0
BEGIN:VEVENT
ORGANIZER:mailto:foo1@example.com
ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:mailto:foo1@example.com
ATTENDEE;RSVP=YES;CUTYPE=INDIVIDUAL:mailto:foo2@example.com
DTSTAMP:19970611T190000Z
DTSTART:19970701T180000Z
DTEND:19970701T183000Z
SUMMARY:Phone Conference
UID:calsvr.example.com-8739701987387771
ATTACH:cid:123456789@example.com
SEQUENCE:0
STATUS:CONFIRMED
END:VEVENT
END:VCALENDAR
--boundary-example-1
Content-Type: application/msword; name="FieldReport.doc"
Content-Transfer-Encoding: base64
Content-Disposition: inline; filename="FieldReport.doc"
Content-ID: <123456789@example.com>
0M8R4KGxGuEAAAAAAAAAAAAAAAAAAAAAPgADAP7/CQAGAAAAAAAAAAABAAAARAAAAAAA
AAAAEAAAQAAAAAEAAAD+////AAAAAEUAAAD/////////////////////////////////
...
--boundary-example-1--
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4.4. Multiple Similar Components
Multiple iCalendar components of the same type can be included in the
iCalendar object when the "METHOD" is the same for each component.
From: foo1@example.com
To: foo2@example.com
Subject: Summer Company Holidays
Mime-Version: 1.0
Content-Type: text/calendar; method=PUBLISH; charset=US-ASCII
Content-Transfer-Encoding: 7bit
Content-Disposition: attachment; filename="event.ics"
BEGIN:VCALENDAR
PRODID:-//Example/ExampleCalendarClient//EN
METHOD:PUBLISH
VERSION:2.0
BEGIN:VEVENT
ORGANIZER:mailto:foo1@example.com
DTSTAMP:19970611T150000Z
DTSTART:19970701T150000Z
DTEND:19970701T230000Z
SUMMARY:Company Picnic
DESCRIPTION:Food and drink will be provided
UID:calsvr.example.com-873970198738777-1
SEQUENCE:0
STATUS:CONFIRMED
END:VEVENT
BEGIN:VEVENT
ORGANIZER:mailto:foo1@example.com
DTSTAMP:19970611T190000Z
DTSTART:19970715T150000Z
DTEND:19970715T230000Z
SUMMARY:Company Bowling Tournament
DESCRIPTION:We have 10 lanes reserved
UID:calsvr.example.com-873970198738777-2
SEQUENCE:0
STATUS:CONFIRMED
END:VEVENT
END:VCALENDAR
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4.5. Multiple Mixed Components
Different component types must be encapsulated in separate iCalendar
objects.
From: foo1@example.com
To: foo2@example.com
Subject: Phone Conference
Mime-Version: 1.0
Content-Type: multipart/mixed;
boundary="--FEE3790DC7E35189CA67CE2C"
This is a multi-part message in MIME format.
----FEE3790DC7E35189CA67CE2C
Content-Type: text/calendar; method=REQUEST; charset=US-ASCII
Content-Transfer-Encoding: 7bit
Content-Disposition: attachment; filename="event1.ics"
BEGIN:VCALENDAR
PRODID:-//Example/ExampleCalendarClient//EN
METHOD:REQUEST
VERSION:2.0
BEGIN:VEVENT
ORGANIZER:mailto:foo1@example.com
ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:mailto:foo1@example.com
ATTENDEE;RSVP=YES;CUTYPE=INDIVIDUAL:mailto:foo2@example.com
DTSTAMP:19970611T190000Z
DTSTART:19970701T210000Z
DTEND:19970701T230000Z
SUMMARY:Phone Conference
DESCRIPTION:Discuss what happened at the last meeting
UID:calsvr.example.com-8739701987387772
SEQUENCE:0
STATUS:CONFIRMED
END:VEVENT
END:VCALENDAR
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----FEE3790DC7E35189CA67CE2C
Content-Type: text/calendar; method=REQUEST; charset=US-ASCII
Content-Transfer-Encoding: 7bit
Content-Disposition: attachment; filename="todo1.ics"
BEGIN:VCALENDAR
PRODID:-//Example/ExampleCalendarClient//EN
METHOD:REQUEST
VERSION:2.0
BEGIN:VTODO
DUE:19970701T160000Z
ORGANIZER:mailto:foo1@example.com
ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:mailto:foo1@example.com
ATTENDEE;RSVP=YES:mailto:foo2@example.com
SUMMARY:Phone Conference
DESCRIPTION:Discuss a new location for the company picnic
UID:calsvr.example.com-td-8739701987387773
SEQUENCE:0
STATUS:NEEDS-ACTION
END:VEVENT
END:VCALENDAR
----FEE3790DC7E35189CA67CE2C
4.6. Detailed Components with an ATTACH Property
This example shows the format of a message containing a group meeting
between three individuals. The "multipart/related" encapsulation is
used because the iCalendar object contains an ATTACH property that
uses a CID to reference the attachment.
From: foo1@example.com
MIME-Version: 1.0
To: foo2@example.com,foo3@example.com
Subject: REQUEST - Phone Conference
Content-Type: multipart/related;
boundary="--FEE3790DC7E35189CA67CE2C"
----FEE3790DC7E35189CA67CE2C
Content-Type: multipart/alternative;
boundary="--00FEE3790DC7E35189CA67CE2C00"
Melnikov Standards Track [Page 16]RFC 6047 iMIP December 2010
----00FEE3790DC7E35189CA67CE2C00
Content-Type: text/plain; charset=us-ascii
Content-Transfer-Encoding: 7bit
When: 7/1/1997 10:00PM PDT - 7/1/97 10:30 PM PDT
Where:
Organizer: foo1@example.com
Summary: Let's discuss the attached document
----00FEE3790DC7E35189CA67CE2C00
Content-Type: text/calendar; method=REQUEST; charset=US-ASCII;
Component=vevent
Content-Transfer-Encoding: 7bit
Content-Disposition: attachment; filename="event.ics"
BEGIN:VCALENDAR
PRODID:-//Example/ExampleCalendarClient//EN
METHOD:REQUEST
VERSION:2.0
BEGIN:VEVENT
ORGANIZER:foo1@example.com
ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:foo1@example.com
ATTENDEE;RSVP=YES;CUTYPE=INDIVIDUAL:mailto:foo2@example.com
ATTENDEE;RSVP=YES;CUTYPE=INDIVIDUAL:mailto:foo3@example.com
DTSTAMP:19970611T190000Z
DTSTART:19970621T170000Z
DTEND:199706211T173000Z
SUMMARY:Let's discuss the attached document
UID:calsvr.example.com-873970198738777-8aa
ATTACH:cid:calsvr.example.com-12345aaa
SEQUENCE:0
STATUS:CONFIRMED
END:VEVENT
END:VCALENDAR
----00FEE3790DC7E35189CA67CE2C00
Melnikov Standards Track [Page 17]RFC 6047 iMIP December 2010
----FEE3790DC7E35189CA67CE2C
Content-Type: application/msword; name="FieldReport.doc"
Content-Transfer-Encoding: base64
Content-Disposition: inline; filename="FieldReport.doc"
Content-ID: <calsvr.example.com-12345aaa>
R0lGODdhTAQZAJEAAFVVVd3d3e4AAP///ywAAAAATAQZAAAC/5yPOSLhD6OctNqLs94Xq
AG4kiW5omm6sq27gvH8kzX9o1y+s73/g8MCofEovGITCoxKMbyCR16cNSq9YrNarfcrvd
riIH5LL5jE6rxc3G+v2cguf0uv2Oz+v38L7/DxgoOKjURnjIIbe3yNjo+AgZWYVIWWl5i
ZnJY6J
...
----FEE3790DC7E35189CA67CE2C
5. Recommended Practices
This section outlines a series of recommended practices when using a
messaging transport to exchange iCalendar objects.
5.1. Use of Content and Message IDs
The [iCAL] specification makes frequent use of the URI for data types
in properties such as "DESCRIPTION", "ATTACH", "CONTACT", and others.
Two forms of URIs are the Message ID (MID) and the Content-ID (CID).
These are defined in [RFC2392]. Although [RFC2392] allows
referencing messages or MIME body parts in other MIME entities or
stores, it is strongly RECOMMENDED that iMIP implementations include
all referenced messages and body parts in a single MIME entity.
Simply put, if an iCalendar object contains CID or MID references to
other messages or body parts, implementations should ensure that
these messages and/or body parts are transmitted with the iCalendar
object. If they are not, there is no guarantee that the receiving
CUA will have the access or the authorization to view those objects.
6. IANA Considerations
The "text/calendar" MIME media type was registered in [iCAL].
Melnikov Standards Track [Page 18]RFC 6047 iMIP December 2010
7. References
7.1. Normative References
[iCAL] Desruisseaux, B., Ed., "Internet Calendaring and
Scheduling Core Object Specification (iCalendar)",
RFC 5545, September 2009.
[iTIP] Daboo, C., Ed., "iCalendar Transport-Independent
Interoperability Protocol (iTIP)", RFC 5546, December
2009.
[RFC5322] Resnick, P., Ed., "Internet Message Format", RFC 5322,
October 2008.
[MAILTO] Duerst, M., Masinter, L., and J. Zawinski, "The 'mailto'
URI Scheme", RFC 6068, October 2010.
[RFC1847] Galvin, J., Murphy, S., Crocker, S., and N. Freed,
"Security Multiparts for MIME: Multipart/Signed and
Multipart/Encrypted", RFC 1847, October 1995.
[RFC2045] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part One: Format of Internet Message
Bodies", RFC 2045, November 1996.
[RFC2046] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part Two: Media Types", RFC 2046,
November 1996.
[RFC2392] Levinson, E., "Content-ID and Message-ID Uniform Resource
Locators", RFC 2392, August 1998.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[UTF-8] Yergeau, F., "UTF-8, a transformation format of ISO
10646", STD 63, RFC 3629, November 2003.
[SMTP-TLS] Hoffman, P., "SMTP Service Extension for Secure SMTP over
Transport Layer Security", RFC 3207, February 2002.
[IMAP-POP-TLS]
Newman, C., "Using TLS with IMAP, POP3 and ACAP",
RFC 2595, June 1999.
Melnikov Standards Track [Page 19]RFC 6047 iMIP December 2010
[RFC5750] Ramsdell, B. and S. Turner, "Secure/Multipurpose Internet
Mail Extensions (S/MIME) Version 3.2 Certificate
Handling", RFC 5750, January 2010.
[RFC5751] Ramsdell, B. and S. Turner, "Secure/Multipurpose Internet
Mail Extensions (S/MIME) Version 3.2 Message
Specification", RFC 5751, January 2010.
[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation
List (CRL) Profile", RFC 5280, May 2008.
7.2. Informative References
[8BITMIME] Klensin, J., Freed, N., Rose, M., Stefferud, E., and D.
Crocker, "SMTP Service Extension for 8bit-MIMEtransport",
RFC 1652, July 1994.
[RFC5598] Crocker, D., "Internet Mail Architecture", RFC 5598, July
2009.
[RFC3282] Alvestrand, H., "Content Language Headers", RFC 3282, May
2002.
Melnikov Standards Track [Page 20]RFC 6047 iMIP December 2010
Appendix A. Changes since RFC 2447
Updated references. Split them into Normative and Informative.
Updated examples to use example.com/example.net domains.
Corrected usage of RFC 2119 language.
Clarified that charset=UTF-8 is required, unless the calendar can be
entirely represented in US-ASCII.
Clarified that 7-bit content transfer encodings should be used unless
the calendar object is known to be transferred over 8-bit clean
transport.
Clarified that file extension specified in the Content-Disposition
header field is not to be used to override the "Content-Type" MIME
type.
Disallowed use of "multipart/alternative" for slightly different
representations of the same calendar.
Clarified handling of the "method" MIME parameter of the "Content-
Type" header field.
Clarified that in an iMIP message an ORGANIZER/ATTENDEE property
contains a mailto: URI.
Fixed examples with ATTENDEE property to use "CUTYPE=" instead of
"TYPE=".
Clarified that message integrity/confidentiality should be achieved
using S/MIME.
Provided additional examples.
Improved the Security Considerations section.
Made multiple editorial changes to different sections of the
document.
Melnikov Standards Track [Page 21]
RFC 6047 iMIP December 2010
Appendix B. Acknowledgements
The editor of this document wishes to thank Frank Dawson, Steve
Mansour, and Steve Silverberg, the original authors of RFC 2447, as
well as the following individuals who have participated in the
drafting, review, and discussion of this memo:
Reinhold Kainhofer, Cyrus Daboo, Bernard Desruisseaux, Eliot Lear,
and Peter Saint-Andre.
Author's Address
Alexey Melnikov (editor)
Isode Ltd
5 Castle Business Village
36 Station Road
Hampton, Middlesex TW12 2BX
UK
EMail: Alexey.Melnikov@isode.com
Melnikov Standards Track [Page 22]
