UCL Technical Report 120
Mailgroup Note 19
Network Working Group S.E. Kille
Request for Comments: 987 University College London
June 1986
Mapping between X.400 and RFC 822
Status of This Memo
This RFC suggests a proposed protocol for the ARPA-Internet
community, and requests discussion and suggestions for improvements.
Distribution of this memo is unlimited.
This document describes a set of mappings which will enable
interworking between systems operating the CCITT X.400 (1984) series
of protocols [CCITT84a], and systems using the RFC 822 mail protocol
[Crocker82a], or protocols derived from RFC 822. The approach aims
to maximise the services offered across the boundary, whilst not
requiring unduly complex mappings. The mappings should not require
any changes to end systems.
This specification should be used when this mapping is performed on
the ARPA-Internet or in the UK Academic Community. This
specification may be modified in the light of implementation
experience, but no substantial changes are expected.
Kille [Page 1]
RFC 987 June 1986
Mapping between X.400 and RFC 822
Chapter 1 -- Overview
1.1. X.400
The X.400 series protocols have been defined by CCITT to provide
an Interpersonal Messaging Service (IPMS), making use of a store
and forward Message Transfer Service. It is expected that this
standard will be implemented very widely. As well as the base
standard (X.400), work is underway on various functional standards
of profiles which specify how X.400 will be used in various
communities. Many of the major functional standards (e.g. from
CEPT, CEN/CENELEC, and NBS) are likely to be similar. Some of the
decisions in this document are in the light of this work. No
reference is given, as these documents are not currently stable.
1.2. RFC 822
RFC 822 evolved as a messaging standard on the DARPA (the US
Defense Advanced Research Projects Agency) Internet. It is
currently used on the ARPA-Internet in conjunction with two other
standards: RFC 821, also known as Simple Mail Transfer Protocol
(SMTP) [Postel82a], and RFC 920 which is a specification for a
domain name system and a distributed name service [Postel84a].
RFC 822, or protocols derived from RFC 822 are used in a number of
other networks. In particular:
UUCP Networks
UUCP is the UNIX to UNIX CoPy protocol <0>, which is usually
used over dialup telephone networks to provide a simple
message transfer mechanism. There are some extensions to
RFC 822, particularly in the addressing. They are likely to
use domains which conform to RFC 920, but not the
corresponding domain nameservers [Horton86a].
CSNET
Some portions of CSNET will follow the ARPA-Internet
protocols. The dialup portion of CSNET uses the Phonenet
protocols as a replacement for RFC 821. This portion is
likely to use domains which conform to RFC 920, but not the
corresponding domain nameservers.
BITNET
Some parts of BITNET use RFC 822 related protocols, with
EBCDIC encoding.
Kille [Page 2]
RFC 987 June 1986
Mapping between X.400 and RFC 822
JNT Mail Networks
A number of X.25 networks, particularly those associated
with the UK Academic Community, use the JNT (Joint Network
Team) Mail Protocol, also known as Greybook [Kille84a].
This is used with domains and name service specified by the
JNT NRS (Name Registration Scheme) [Larmouth83a].
The mappings specified here are appropriate for all of these
networks.
1.3. The Need for Conversion
There is a large community using RFC 822 based protocols for mail
services, who will wish to communicate with X.400 systems. This
will be a requirement, even in cases where communities intend to
make a transition to use of X.400, where conversion will be needed
to ensure a smooth service transition. It is expected that there
will be more than one gateway <1>, and this specification will
enable them to behave in a consistent manner. These gateways are
sometimes called mail relays. Consistency between gateways is
desirable to provide:
1. Consistent service to users.
2. The best service in cases where a message passes through
multiple gateways.
1.4. General Approach
There are a number of basic principles underlying the details of
the specification.
1. The specification should be pragmatic. There should not
be a requirement for complex mappings for 'Academic'
reasons. Complex mappings should not be required to
support trivial additional functionality.
2. Subject to 1), functionality across a gateway should be as
high as possible.
3. It is always a bad idea to lose information as a result of
any transformation. Hence, it is a bad idea for a gateway
to discard information in the objects it processes. This
includes requested services which cannot be fully mapped.
4. All mail gateways actually operate at exactly one level
Kille [Page 3]
RFC 987 June 1986
Mapping between X.400 and RFC 822
above the layer on which they conceptually operate. This
implies that the gateway must not only be cognisant of the
semantics of objects at the gateway level, but also be
cognisant of higher level semantics. If meaningful
transformation of the objects that the gateway operates on
is to occur, then the gateway needs to understand more
than the objects themselves.
1.5. Gatewaying Model
1.5.1. X.400
The CCITT X.400 series recommendations specify a number of
services and protocols. The services are specified in X.400.
Two of these services are fundamental to this document:
1. The Message Transfer Service, which can be provided by
either the P1 or P3 protocols, which are specified in
X.411 [CCITT84b]. This document talks in terms of P1,
but the mappings are equally applicable to P3.
2. The Interpersonal Messaging Service (IPMS), which is
provided by the P2 protocol specified in X.420
[CCITT84c].
This document considers only IPMS, and not of any other usage
of the Message Transfer Service. This is reasonable, as
RFC 822, broadly speaking, provides a service corresponding to
IPMS, and no services other than IPMS have been defined over
the Message Transfer Service. As none of the RTS (Reliable
Transfer Service) service elements is available to the IPMS
user, this level and lower levels are of no concern in this
gatewaying specification. Note that in this memo "IP" means
"InterPersonal" (not Internet Protocol).
The Message Transfer Service defines an end-to-end service over
a series of Message Transfer Agents (MTA). It also defines a
protocol, P1, which is used between a pair of MTAs. This
protocol is simply a file format (Message Protocol Data Unit,
or MPDU), transferred between two MTAs using the RTS. There
are three types of MPDU:
User MPDU
This contains envelope information, and uninterpreted
contents. The envelope includes an ID, an originator, a
Kille [Page 4]
RFC 987 June 1986
Mapping between X.400 and RFC 822
list of recipients, and trace information. It is used to
carry data for higher level services.
Probe
This contains only envelope information. It is used to
determine whether a User UMPDU could be delivered to a
given O/R (originator/recipient) name.
Delivery Report
This contains envelope information, and specified
contents. It is used to indicate delivery success or
failure of a User or Probe MPDU over the Message Transfer
Service.
IPMS (P2) specifies two content types for the P1 User MPDU
(User Agent Protocol Data Units or UAPDU):
Interpersonal Message (IM-UAPDU)
This has two components: a heading, and a body. The body
is structured as a sequence of body parts, which may be
basic components (e.g.IA5 text, or G3 fax), or IP
Messages. The header contains end to end user
information, such as subject, primary recipients (To:),
and priority. The validity of these fields is not
guaranteed by the Message Transfer Service. This
provides the basic IPMS.
Status Report (SR-UAPDU)
This UAPDU has defined contents. It is used to indicate
that a message has been received by a User Agent. It
does not have to be implemented.
1.5.2. RFC 822
RFC 822 is based on the assumption that there is an underlying
service, which is here called the 822-P1 service. The 822-P1
service provides three basic functions:
1. Identification of a list of recipients.
2. Identification of an error return address.
3. Transfer of an RFC 822 message.
Kille [Page 5]
RFC 987 June 1986
Mapping between X.400 and RFC 822
It is possible to achieve 2) within the RFC 822 header. Some
822-P1 protocols, in particular SMTP, can provide additional
functionality, but as these are neither mandatory in SMTP, nor
available in other 822-P1 protocols, they are not considered
here. Details of aspects specific to a number of 822-P1
protocols are given in appendices B to E. An RFC 822 message
consists of a header, and content which is uninterpreted ASCII
text. The header is divided into fields, which are the
protocol elements. Most of these fields are analogous to P2
header elements, although some are analogous to P1 envelope
elements.
1.5.3. The Gateway
Given this functional description of the two protocols, the
functional nature of a gateway can now be considered. It would
be elegant to consider the 822-P1 service mapping onto P1 and
RFC 822 mapping onto P2, but reality just does not fit.
Therefore one must consider that P1 or P1 + P2 on one side are
mapped into RFC 822 + 822-P1 on the other in a slightly tangled
manner. The details of the tangle will be made clear in
chapter 5. The following basic mappings are thus proposed.
When going from RFC 822 to X.400, an RFC 822 message and the
associated 822-P1 information is always mapped into an IM-UAPDU
and the associated P1 envelope. Going from X.400 to RFC 822,
an RFC 822 message and the associated 822-P1 information may be
derived from:
1. A Delivery Report MPDU
2. An SR-UAPDU and the associated P1 envelope.
3. An IM-UAPDU and the associated P1 envelope.
Probe MPDUs must be processed by the gateway - this is
discussed in chapter 5. Any other User MPDUs are not mapped by
the gateway, and should be rejected at the gateway.
Kille [Page 6]
RFC 987 June 1986
Mapping between X.400 and RFC 822
1.6. Document Structure
This document has five chapters:
1. Overview - this document.
2. Service Elements - This describes the (end user) services
mapped by a gateway.
3. Basic mappings - This describes some basic notation used
in chapters 3-5, the mappings between character sets, and
some fundamental protocol elements.
4. Addressing - This considers the mapping between X.400 O/R
names and RFC 822 addresses, which is a fundamental
gateway component.
5. Protocol Elements - This describes the details of all
other mappings.
There are also six appendices:
A. Quoted String Encodings.
B. Mappings Specific to JNT Mail.
C. Mappings Specific to Internet Mail.
D. Mappings Specific to Phonenet Mail.
E. Mappings Specific to UUCP Mail.
F. Format of Address Tables.
1.7. Acknowledgements
This document is eclectic, and credit should be given:
- Study of the EAN X.400 system code which performs this
function [Neufeld85a]. Some detailed clarification was
made by the DFN report on EAN [Bonacker85a].
- An unpublished ICL report, which considered a subset of
the problem [ICL84a].
- A document by Marshall Rose [Rose85a].
Kille [Page 7]
RFC 987 June 1986
Mapping between X.400 and RFC 822
- A document by Mark Horton [Horton85a]. The string
encodings of chapter 3 were derived directly from this
work, as is much of chapter 4.
- Discussion on a number of electronic mailing lists.
- Meetings in the UK and the US.
Kille [Page 8]
RFC 987 June 1986
Mapping between X.400 and RFC 822
Chapter 2 -- Service Elements
RFC 822 and X.400 provide a number of services to the end user. This
document describes the extent to which each service can be supported
across an X.400 <-> RFC 822 gateway. The cases considered are single
transfers across such a gateway, although the problems of multiple
crossings are noted where appropriate.
When a service element is described as supported, this means that
when this service element is specified by a message originator for a
recipient behind a gateway, that it is mapped by the gateway to
provide the service implied by the element. For example, if an
RFC 822 originator specifies a Subject: field, this is considered to
be supported, as an X.400 recipient will get a subject indication.
Support implies:
- Semantic correspondence.
- No loss of information.
- Any actions required by the service element.
For some services, the corresponding protocol elements map well, and
so the service can be fully provided. In other cases, the service
cannot be provided, as there is a complete mismatch. In the
remaining cases, the service can be partially fulfilled. The level
of partial support is summarised.
NOTE: It should be clear that support of service elements on
reception is not a gatewaying issue. It is assumed that all
outbound messages are fully conforming to the appropriate
standards.
2.1. RFC 822
RFC 822 does not explicitly define service elements, as distinct
from protocol elements. However, all of the RFC 822 header
fields, with the exception of trace, can be regarded as
corresponding to implicit RFC 822 service elements. A mechanism
of mapping used in several cases, is to place the text of the
header into the body of the IP Message. This can usually be
regarded as partial support, as it allows the information to be
conveyed to the end user even though there is no corresponding
X.400 protocol element. Support for the various service elements
(headers) is now listed.
Kille [Page 9]
RFC 987 June 1986
Mapping between X.400 and RFC 822
Date:
Supported.
From:
Supported. For messages where there is also a sender field,
the mapping is to "Authorising Addresses", which has subtly
different semantics to the general RFC 822 usage of From:.
Sender:
Supported.
Reply-To:
Supported.
To:
Supported.
Cc:
Supported.
Bcc:
Supported.
Message-Id:
Supported.
In-Reply-To:
Supported, for a single reference in msg-id form. Other
cases are passed in the message text.
References:
Supported.
Keywords:
Passed in the message text.
Kille [Page 10]
RFC 987 June 1986
Mapping between X.400 and RFC 822
Subject:
Supported.
Comments:
Passed in the message text.
Encrypted:
Passed in the message text. This may not be very useful.
Resent-*
Passed in the message text. In principle, these could be
supported in a fuller manner, but this is not suggested.
Other Fields
In particular X-* fields, and "illegal" fields in common
usage (e.g. "Fruit-of-the-day:") are passed in the message
text.
2.2. X.400
When mapping from X.400 to RFC 822, it is not proposed to map any
elements into the body of an RFC 822 message. Rather, new RFC 822
headers are defined. It is intended that these fields will be
registered, and that co-operating RFC 822 systems may use them.
Where these new fields are used, and no system action is implied,
the service can be regarded as being almost supported. Chapter 5
describes how to map these new headers in both directions. Other
elements are provided, in part, by the gateway as they cannot be
provided by RFC 822. Some service elements are are marked N/A
(not applicable). These elements are only applicable to User
Agent / Message Transfer Agent interaction and have no end-to-end
implication. These elements do not need to be mapped by the
gateway.
2.2.1. Message Transfer Service Elements
Access Management
N/A.
Kille [Page 11]
RFC 987 June 1986
Mapping between X.400 and RFC 822
Content Type Indication
Not mapped. As it can only have one value (P2), there is
little use in creating a new RFC 822 header field, unless it
was to distinguish delivery reports.
Converted Indication
Supported by a new RFC 822 header.
Delivery Time Stamp Indication
N/A.
Message Identification
Supported, by use of a new RFC 822 header. This new header
is required, as X.400 has two message-ids whereas RFC 822
has only one.
Non-delivery Notification
Not supported, although in general an RFC 822 system will
return errors as IP messages. In other elements, this
pragmatic result is treated as effective support of this
service element.
Original Encoded Information Types Indication
Supported as a new RFC 822 header.
Registered Encoded Information Types
N/A.
Submission Time Stamp Indication
Supported.
Alternate Recipient Allowed
Not supported. Any value is ignored by the gateway.
Deferred Delivery
Support is optional. The framework is provided so that
messages may be held at the gateway. However, a gateway
Kille [Page 12]
RFC 987 June 1986
Mapping between X.400 and RFC 822
following this specification does not have to do this. This
is in line with the emerging functional standards.
Deferred Delivery Cancellation
Supported.
Delivery Notification
Supported at gateway. Thus, a notification is sent by the
gateway to the originator <2>.
Disclosure of Other Recipients
Supported by use of a new RFC 822 header.
Grade of Delivery Selection
Supported as a new RFC 822 header. In general, this will
only be for user information in the RFC 822 world.
Multi-Destination Delivery
Supported.
Prevention of Non-delivery Notification
Not Supported, as there is no control in the RFC 822 world
(but see Non-delivery Notification).
Return of Contents
This is normally the case, although the user has no control
(but see Non-delivery Notification).
Conversion Prohibition
Supported. Note that in practice this support is restricted
by the nature of the gateway.
Explicit Conversion
Supported, for appropriate values (See the IPMS Typed Body
service element).
Kille [Page 13]
RFC 987 June 1986
Mapping between X.400 and RFC 822
Implicit Conversion
Supported, in the sense that there will be implicit
conversion to IA5 in cases where this is practical.
Probe
Supported at the gateway (i.e. the gateway services the
probe).
Alternate Recipient Assignment
N/A.
Hold for Delivery
N/A.
2.2.2. Interpersonal Message Service Elements
IP-message Identification
Supported.
Typed Body
Supported. IA5 is fully supported. ForwardedIPMessage is
supported, with some loss of information. A subset of TTX
is supported (see section 5 for the specification of this
subset), with some loss of information. SFD may be
supported, with some loss of information. TTX and SFD are
only supported when conversion is allowed. Other types are
not supported.
Blind Copy Recipient Indication
Supported.
Non-receipt Notification
Not supported.
Receipt Notification
Not supported.
Kille [Page 14]
RFC 987 June 1986
Mapping between X.400 and RFC 822
Auto-forwarded Indication
Supported as new RFC 822 header.
Originator Indication
Supported.
Authorising User's Indication
Supported, although the mapping (From:) is not quite the
same.
Primary and Copy Recipients Indication
Supported.
Expiry Date Indication
Supported as new RFC 822 header. In general, only human
action can be expected.
Cross Referencing Indication
Supported.
Importance Indication
Supported as new RFC 822 header.
Obsoleting Indication
Supported as new RFC 822 header.
Sensitivity Indication
Supported as new RFC 822 header.
Subject Indication
Supported.
Reply Request Indication
Supported as comment next to address.
Kille [Page 15]
RFC 987 June 1986
Mapping between X.400 and RFC 822
Forwarded IP-message Indication
Supported, with some loss of information.
Body Part Encryption Indication
Not supported.
Multi-part Body
Supported, with some loss of information, in that the
structuring cannot be formalised in RFC 822.
Kille [Page 16]
RFC 987 June 1986
Mapping between X.400 and RFC 822
Chapter 3 -- Basic Mappings
3.1. Notation
The P1 and P2 protocols are encoded in a structured manner
according to the X.409 specifications, whereas RFC 822 is text
encoded. To define a detailed mapping, it is necessary to refer
to detailed protocol elements in each format. This is described.
3.1.4. RFC 822
Structured text is defined according to the Extended Backus
Naur Form (EBNF) defined in section 2 of RFC 822 [Crocker82a].
In the EBNF definitions used in this specification, the syntax
rules given in Appendix D of RFC 822 are assumed. When these
EBNF tokens are referred to outside an EBNF definition, they
are identified by the string "882." appended to the beginning
of the string (e.g. 822.addr-spec). Additional syntax rules,
to be used throughout this specification are defined in this
chapter.
The EBNF is used in two ways.
1. To describe components of RFC 822 messages (or of
822-P1 components). In this case, the lexical analysis
defined in section 3 of RFC 822 should be used. When
these new EBNF tokens are referred to outside an EBNF
definition, they are identified by the string "EBNF."
appended to the beginning of the string (e.g.
EBNF.bilateral-info).
2. To describe the structure of IA5 or ASCII information
not in an RFC 822 message. In these cases, tokens will
either be self delimiting, or be delimited by self
delimiting tokens. Comments and LWSP are not used as
delimiters.
3.1.5. X.409
An element is referred to with the following syntax, defined in
EBNF:
element = protocol "." definition *( "." definition )
protocol = "P1" / "P2"
definition = identifier / context
identifier = ALPHA *< ALPHA or DIGIT or "-" >
context = "[" 1*DIGIT "]"
Kille [Page 17]
RFC 987 June 1986
Mapping between X.400 and RFC 822
For example, P2.Heading.subject defines the subject element of
the P2 heading. The same syntax is also used to refer to
element values. For example,
P1.EncodedInformationTypes.[0].g3Fax refers to a value of
P1.EncodedInformationTypes.[0] .
3.2. ASCII and IA5
A gateway will interpret all IA5 as ASCII. Thus, they are treated
identically for the rest of this document.
3.3. Universal Primitives
There is a need to convert between ASCII text, and some of the
Universal Primitive types defined in X.409 [CCITT84d]. For each
case, an EBNF syntax definition is given, for use in all of this
specification. All EBNF syntax definitions of Universal
Primitives are in lower case, whereas X.409 primitives are
referred to with the first letter in upper case. Except as noted,
all mappings are symmetrical.
3.3.1. Boolean
Boolean is encoded as:
boolean = "TRUE" / "FALSE"
3.3.2. NumericString
NumericString is encoded as:
numericstring = *DIGIT
3.3.3. PrintableString
PrintableString is a restricted IA5String defined as:
printablestring = *( ps-char / ps-delim )
ps-char = 1DIGIT / 1ALPHA / " " / "'" / "+" / ")"
/ "," / "-" / "." / "/" / ":" / "=" / "?"
ps-delim = "("
A structured subset of EBNF.printablestring is now defined.
This can be used to encode ASCII in the PrintableString
character set.
Kille [Page 18]
RFC 987 June 1986
Mapping between X.400 and RFC 822
ps-encoded = *( ps-char / ps-encoded-char )
ps-encoded-char = "(a)" ; (@)
/ "(p)" ; (%)
/ "(b)" ; (!)
/ "(q)" ; (")
/ "(u)" ; (_)
/ "(" 3DIGIT ")"
The 822.3DIGIT in EBNF.ps-encoded-char must have range 0-127
(Decimal), and is interpreted in decimal as the corresponding
ASCII character. Special encodings are given for: at sign (@),
percent (%), exclamation mark/bang (!), double quote ("), and
underscore (_). These characters are not included in
PrintableString, but are common in RFC 822 addresses. The
abbreviations will ease specification of RFC 822 addresses from
an X.400 system.
An asymmetric mapping between PrintableString and ASCII can now
be defined <3>. To encode ASCII as PrintableString, the
EBNF.ps-encoded syntax is used, with all EBNF.ps-char AND
EBNF.ps-delim mapped directly <4>. All other 822.CHAR are
encoded as EBNF.ps-encoded-char. There are two cases of
encoding PrintableString as ASCII. If the PrintableString can
be parsed as EBNF.ps-encoded, then the previous mapping should
be reversed. If not, it should be interpreted as
EBNF.printablestring.
Some examples are now given. Note the arrows which indicate
asymmetrical mappings:
PrintableString ASCII
'a demo.' <-> 'a demo.'
foo(a)bar <-> foo@bar
(q)(u)(p)(q) <-> "_%"
(a) <-> @
(a) <- (a)
(040)a(041) -> (a)
(040)(a) -> (@
((a) <- (@
The algorithm is designed so that it is simple to use in all
common cases, so that it is general, and so that it is
straightforward to code. It is not attempting to minimise the
number of pathological cases.
Kille [Page 19]
RFC 987 June 1986
Mapping between X.400 and RFC 822
3.3.4. T.61String
T.61 strings are, in general, only used for conveying human
interpreted information. Thus, the aim of a mapping should be
to render the characters appropriately in the remote character
set, rather than to maximise reversibility. The mappings
defined in the CEN/CENELEC X.400 functional standard should be
used [CEN/CENELEC/85a]. These are based on the mappings of
X.408 (sections 4.2.2 and 5.2.2).
3.3.5. UTCTime
Both UTCTime and the RFC 822 822.date-time syntax contain: Year
(lowest two digits), Month, Day of Month, hour, minute, second
(optional), and Timezone. 822.date-time also contains an
optional day of the week, but this is redundant. Therefore a
symmetrical mapping can be made between these constructs <5>.
The UTCTime format which specifies the timezone offset should
be used, in line with CEN/CENELEC recommendations.
Kille [Page 20]
RFC 987 June 1986
Mapping between X.400 and RFC 822
Chapter 4 -- Addressing
Addressing is probably the trickiest problem of an X.400 <-> RFC 822
gateway. Therefore it is given a separate chapter. This chapter, as
a side effect, also defines a standard textual representation of
X.400 addresses.
Initially we consider an address in the (human) mail user sense of
"what is typed at the mailsystem to reference a human". A basic
RFC 822 address is defined by the EBNF EBNF.822-address:
822-address = [ route ] addr-spec
In an 822-P1 protocol, the originator and each recipient should be
considered to be defined by such a construct. In an RFC 822 header,
the EBNF.822-address is encapsulated in the 822.address syntax rule,
and there may also be associated comments. None of this extra
information has any semantics, other than to the end user.
The basic X.400 address is defined by P1.ORName. In P1 all recipient
P1.ORnames are encapsulated within P1.RecipientInfo, and in P2 all
P2.ORNames <6> are encapsulated within P2.ORDescriptor.
It can be seen that RFC 822 822.address must be mapped with
P2.ORDescriptor, and that RFC 822 EBNF.822-address must be mapped
with P1.ORName (originator) and P1.RecipientInfo (recipients).
This chapter is structured as follows:
4.1 Introduction.
4.2 A textual representation of P1.ORName. This is needed for
the later mappings, and as a side effect provides a standard
representation for O/R names.
4.3 Mapping between EBNF.822-address and P1.ORName
4.4 The Full P1 / 822-P1 Mapping
4.5 The Full P2 / RFC 822 Mapping
4.6 Mapping Message-IDs.
Kille [Page 21]
RFC 987 June 1986
Mapping between X.400 and RFC 822
4.1. A textual representation of P1.ORName.
P1.ORName is structured as a set of attribute value pairs. It is
clearly necessary to be able to encode this in ASCII for
gatewaying purposes. A general encoding is given here, which may
be used as a basis for a user interface, as well as for the
defined gateway mapping.
4.1.1. Basic Representation
A series of BNF definitions of each possible attribute value
pair is given, which is given a 1:1 mapping with the X.400
encoding. The rest of the mapping then talks in terms of these
BNF components, with the mapping to X.400 encoding being
trivial.
attributevalue = c / admd / prmd / x121 / t-id / o / ou
/ ua-id / pn.g / pn.i / pn.s / pn.gq / dd.value
c = printablestring ; P1.CountryName
admd = printablestring ; P1.AdministrationDomainName
prmd = printablestring ; P1.PrivateDomainName
x121 = numericstring ; P1.X121Address
t-id = numericstring ; P1.TerminalID
o = printablestring ; P1.OrganisationName
ou = printablestring ; P1.OrganisationalUnit
ua-id = numericstring ; P1.UniqueUAIdentifier
pn.s = printablestring ; P1.PersonalName.surName
pn.g = printablestring ; P1.PersonalName.givenName
pn.i = printablestring ; P1.PersonalName.initials
pn.gq = printablestring ; P1.PersonalName.generation
Qualifier
dd.value = printablestring ; P1.DomainDefined
Attribute.value
In cases where an attribute can be encoded as either a
PrintableString or NumericString (Country, ADMD, PRMD) it is
assumed that the NumericString encoding will be adopted if
possible. This prevents the encoding of PrintableString where
the characters are all numbers. This restriction seems
preferable to the added complexity of a general solution.
Similarly, we can define a set of attribute types.
Kille [Page 22]
RFC 987 June 1986
Mapping between X.400 and RFC 822
dd.type = printablestring ; P1.DomainDefinedAttribute.type
standard-type =
"C" ; P1.CountryName
/ "ADMD" ; P1.AdministrationDomainName
/ "PRMD" ; P1.PrivateDomainName
/ "X121" ; P1.X121Address
/ "T-ID" ; P1.TerminalID
/ "O" ; P1.OrganisationName
/ "OU" ; P1.OrganisationalUnit
/ "UA-ID" ; P1.UniqueUAIdentifier
/ "S" ; P1.PersonalName.surName
/ "G" ; P1.PersonalName.givenName
/ "I" ; P1.PersonalName.initials
/ "GQ" ; P1.PersonalName.generationQualifier
standard-dd-type =
"RFC-822" ; dd.type = "RFC-822"
/ "JNT-Mail" ; dd.type = "JNT-Mail"
/ "UUCP" ; dd.type = "UUCP"
4.1.2. Encoding of Personal Name
Handling of Personal Name based purely on the
EBNF.standard-type syntax defined above is likely to be clumsy.
It seems desirable to utilise the "human" conventions for
encoding these components. A syntax is proposed here. It is
designed to cope with the common cases of O/R Name
specification where:
1. There is no generational qualifier
2. Initials contain only letters <7>.
3. Given Name does not contain full stop ("."), and is at
least two characters long.
4. If Surname contains full stop, then it may not be in
the first two characters, and either initials or given
name is present.
Kille [Page 23]
RFC 987 June 1986
Mapping between X.400 and RFC 822
The following EBNF is defined:
encoded-pn = [ given "." ] *( initial "." ) surname
given = 2*
initial = ALPHA
surname = printablestring
Subject to the above restriction, this is a reversible mapping.
For example:
GivenName = "Marshall"
Surname = "Rose"
Maps with "Marshall.Rose"
Initials = "MT"
Surname = "Rose"
Maps with "M.T.Rose"
GivenName = "Marshall"
Initials = "MT"
Surname = "Rose"
Maps with "Marshall.M.T.Rose"
Note that CCITT guidelines suggest that Initials is used to
encode ALL initials. Therefore, the proposed encoding is
"natural" when either GivenName or Initials, but not both, are
present. The case where both are present can be encoded, but
this appears to be contrived!
4.1.3. Two encodings of P1.ORName
Given this structure, we can specify a BNF representation of an
O/R Name.
Kille [Page 24]
RFC 987 June 1986
Mapping between X.400 and RFC 822
std-orname = 1*( "/" attribute "=" value ) "/"
attribute = standard-type
/ "PN"
/ standard-dd-type
/ registered-dd-type
/ "DD." std-printablestring
value = std-printablestring
registered-dd-type
= std-printablestring
std-printablestring =
= *( std-char / std-pair )
std-char =
dmn-pair = "\."
For example: C$US.ADMD$ATT.~ROLE$Big\.Chief
Kille [Page 25]
RFC 987 June 1986
Mapping between X.400 and RFC 822
4.2. Mapping between EBNF.822-address and P1.ORName
Ideally, the mapping specified would be entirely symmetrical and
global, to enable addresses to be referred to transparently in the
remote system, with the choice of gateway being left to the
Message Transfer Service. There are two fundamental reasons why
this is not possible:
1. The syntaxes are sufficiently different to make this
awkward.
2. In the general case, there would not be the necessary
administrative co-operation between the X.400 and RFC 822
worlds, which would be needed for this to work.
Therefore, an asymmetrical mapping is defined.
4.2.1. X.400 encoded in RFC 822
The std-orname syntax is used to encode O/R Name information
in the 822.local-part of EBNF.822-address. Further O/R Name
information may be associated with the 822.domain component.
This cannot be used in the general case, basically due to
character set problems, and lack of order in X.400 O/R Names.
The only way to encode the full PrintableString character set
in a domain is by use of the 822.domain-ref syntax. This is
likely to cause problems on many systems. The effective
character set of domains is in practice reduced from the
RFC 822 set, by restrictions imposed by domain conventions and
policy.
A generic 822.address consists of a 822.local-part and a
sequence of 822.domains (e.g.
<@domain1,@domain2:user@domain3>). All except the 822.domain
associated with the 822.local-part (domain3 in this case)
should be considered to specify routing within the RFC 822
world, and will not be interpreted by the gateway (although
they may have identified the gateway from within the RFC 822
world). The 822.domain associated with the 822.local-part may
also identify the gateway from within the RFC 822 world. This
final 822.domain may be used to determine some number of O/R
Name attributes. The following O/R Name attributes are
considered as a hierarchy, and may be specified by the domain.
They are (in order of hierarchy):
Country, ADMD, PRMD, Organisation, Organisational Unit
Kille [Page 26]
RFC 987 June 1986
Mapping between X.400 and RFC 822
There may be multiple Organisational Units.
Associations may be defined between domain specifications, and
some set of attributes. This association proceeds
hierarchically: i.e. if a domain implies ADMD, it also implies
country. If one of the hierarchical components is omitted from
an X.400 structure, this information can be associated with the
corresponding domain (e.g. a domain can be mapped onto a
Country/ADMD/Organisation tuple). Subdomains under this are
associated according to the O/R Name hierarchy. For example:
=> "AC.UK" might be associated with
C="234", ADMD="BT", PRMD="DES"
then domain "R-D.Salford.AC.UK" maps with
C="234", ADMD="BT", PRMD="DES", O="Salford", OU="R-D"
There are two basic reasons why a domain/attribute mapping
might be maintained, as opposed to using simply subdomains:
1. As a shorthand to avoid redundant X.400 information.
In particular, there will often be only one ADMD per
country, and so it does not need to be given
explicitly.
2. To deal with cases where attribute values do not fit
the syntax:
domain-syntax = ALPHA [ *alphanumhyphen alphanum ]
alphanum =
alphanumhyphen =
Although RFC 822 allows for a more general syntax, this
restriced syntax is chosen as it is the one chosen by the
various domain service administrations.
This provides a general aliasing mechanism.
This set of mappings need only be known by the gateways
relaying between the RFC 822 world, and the O/R Name namespace
associated with the mapping in question. However, it is
desirable (for the optimal mapping of third party addresses)
for all gateways to know these mappings. A format for the
exchange of this information is defined in Appendix F.
From the standpoint of the RFC 822 Message Transfer System, the
domain specification is simply used to route the message in the
Kille [Page 27]
RFC 987 June 1986
Mapping between X.400 and RFC 822
standard manner. The standard domain mechanisms are used to
identify gateways, and are used to select appropriate gateways
for the corresponding O/R Name namespace. In most cases, this
will be done by registering the higher levels, and assuming
that the gateway can handle the lower levels.
As a further mechanism to simplify the encoding of common
cases, where the only attributes to be encoded on the LHS are
Personal Name attributes which comply with the restrictions of
4.2.2, the 822.local-part may be encoded as EBNF.encoded-pn.
An example encoding is:
/PN=J.Linnimouth/GQ=5/@Marketing.Xerox.COM
encodes the P1.ORName consisting of
P1.CountryName = "US"
P1.AdministrationDomainName = "ATT"
P1.OrganisationName = "Xerox"
P1.OrganisationalUnit = "Marketing"
P1.PersonalName.surName = "Linnimouth"
P1.PersonalName.initials = "J"
P1.PersonalName.GenerationQualifier = "5"
If the GenerationQualifier was not present, the encoding
J.Linnimouth@Marketing.Xerox.COM could be used.
Note that in this example, the first three attributes are
determined by the domain Xerox.COM. The OrganisationalUnit is
determined systematically.
There has been an implicit assumption that an RFC 822 domain is
either X.400 or RFC 822. This is pragmatic, but undesirable,
as the namespace should be structured on a logical basis which
does not necessarily correspond to the choice of Message
Transfer protocols. The restriction can be lifted, provided
that the nameservice deals with multiple message transfer
protocols. This can happen in a straightforward manner for the
UK NRS, as explained in [Kille86a]. It could also be achieved
with the DARPA Domain Nameserver scheme by use of the WKS
mechanism.
Kille [Page 28]
RFC 987 June 1986
Mapping between X.400 and RFC 822
4.2.2. RFC 822 Encoded in X.400
In some cases, the encoding defined above may be reversed, to
give a "natural" encoding of genuine RFC 822 addresses. This
depends largely on the allocation of appropriate management
domains.
The general case is mapped by use of domain defined attributes.
Three are defined, according to the full environment used to
interpret the RFC 822 information.
1. Domain defined type "RFC-822". This string is to be
interpreted in the context of RFC 822, and RFC 920
[Crocker82a,Postel84a].
2. Domain defined type "JNT-Mail". This string is to be
interpreted in the context of the JNT Mail protocol,
and the NRS [Kille84a,Larmouth83a].
3. Domain defined type "UUCP". This is interpreted
according to the constraints of the UUCP world
[Horton86a].
These three are values currently known to be of use. Further
recognised values may be defined. These will be maintained in
a list at the SRI Network Information Center.
Other O/R Name attributes will be used to identify a context in
which the O/R Name will be interpreted. This might be a
Management Domain, or some part of a Management Domain which
identifies a gateway MTA. For example:
1)
C = "GB"
ADMD = "BT"
PRMD = "AC"
"JNT-Mail" = "Jimmy(a)UK.CO.BT-RESEARCH-LABS"
2)
C = "US"
ADMD = "Telemail"
PRMD = "San Fransisco"
O = "U Cal"
OU = "Berkeley"
"RFC-822" = "postel(a)usc-isib.arpa"
Kille [Page 29]
RFC 987 June 1986
Mapping between X.400 and RFC 822
Note in each case the PrintableString encoding of "@" as "(a)".
In the first example, the "JNT-Mail" domain defined attribute
is interpreted everywhere within the (Administrative or
Private) Management Domain. In the second example, further
attributes are needed within the Management Domain to identify
a gateway. Thus, this scheme can be used with varying levels
of Management Domain co-operation.
4.2.3. RFC 822 -> X.400
There are two basic cases:
1. X.400 addresses encoded in RFC 822. This will also
include RFC 822 addresses which are given reversible
encodings.
2. "Genuine" RFC 822 addresses.
The mapping should proceed as follows, by first assuming case
1).
STAGE 1.
1. If the 822-address is not of the form:
local-part "@" domain
go to stage 2.
2. Attempt to parse domain as:
*( domain-syntax "." ) known-domain
Where known-domain is the longest possible match in a
list of gatewayed domains. If this fails, and the domain
does not explicitly identify the local gateway, go to
stage 2. If it succeeds, allocate the attributes
associated with EBNF.known-domain, and systematically
allocate the attributes implied by each
EBNF.domain-syntax component.
3. Map 822.local-part to ASCII, according to the
definition of Appendix A. This step should be applied:
A. If the source network cannot support
822.quoted-string (as discussed in Appendix A).
Kille [Page 30]
RFC 987 June 1986
Mapping between X.400 and RFC 822
B. If the address is an 822-P1 recipient.
This mapping is always applied in case B, as it
increases the functionality of the gateway, and does
not imply any loss of generality. Mapping case B
allows sites which cannot generate 822.quoted-string
to address recipients the gateway, without the gateway
having to know this explicitly. There is no loss of
functionality, as the quoting character of Appendix A
(#) is not in PrintableString. This seems desirable.
It should not be applied in to other addresses, as a
third party RFC#822 address containing the sequence
EBNF.atom-encoded (as defined in Appendix A) would be
transformed asymmetrically.
4. Map the result of 3) to EBNF.ps-encoded according to
section 3.
5. Parse the result of 4) according to the EBNF
EBNF.std-orname. If this parse fails, parse the result
of 4) according to the EBNF EBNF.encoded-pn. If this
also fails, go to stage 2. Otherwise, the result is a
set of type/value pairs.
6. Associate the EBNF.attribute-value syntax (determined
from the identified type) with each value, and check
that it conforms. If not, go to stage 2.
7. Ensure that the set of attributes conforms both to the
X.411 P1.ORName specification and to the restrictions
on this set given in X.400. If not go to stage 2.
8. Build the O/R Name from this information.
STAGE 2.
This will only be reached if the RFC 822 EBNF.822-address is
not a valid X.400 encoding. If the address is an 822-P1
recipient address, it must be rejected, as there is a need to
interpret such an address in X.400. For the 822-P1 return
address, and any addresses in the RFC 822 header, they should
now be encoded as RFC 822 addresses in an X.400 O/R Name:
1. Convert the EBNF.822-address to PrintableString, as
specified in chapter 3.
2. The domain defined attribute ("RFC-822", "JNT-Mail" or
Kille [Page 31]
RFC 987 June 1986
Mapping between X.400 and RFC 822
"UUCP") appropriate to the gateway should be selected,
and its value set.
3. Build the rest of the O/R Name in the local Management
Domain agreed manner, so that the O/R Name will receive
a correct global interpretation.
4.2.4. X.400 -> RFC 822
There are two basic cases:
1. RFC 822 addresses encoded in X.400.
2. "Genuine" X.400 addresses. This may include
symmetrically encoded RFC 822 addresses.
When a P1 Recipient O/R Name is interpreted, gatewaying will be
selected if there a single special domain defined attribute
present ("RFC-822", "JNT-Mail" or "UUCP"). In this case, use
mapping A. For other O/R Names which
1. Contain the special attribute.
AND
2. Identify the local gateway with the other attributes.
Use mapping A. In other cases, use mapping B.
Mapping A
1. Map the domain defined attribute value to ASCII, as
defined in chapter 3.
2. Where appropriate (P1 recipients), interpret the string
according to the semantics implied by the domain
defined attribute.
Mapping B.
This will be used for X.400 addresses which do not use the
explicit RFC 822 encoding.
1. Noting the hierarchy specified in 4.3.1, determine the
maximum set of attributes which have an associated
domain specification. If no match is found, allocate
Kille [Page 32]
RFC 987 June 1986
Mapping between X.400 and RFC 822
the domain as the domain specification of the local
gateway, and go to step 4.
2. Following the 4.3.1 hierarchy, if each successive
component exists, and conforms to the syntax
EBNF.domain-syntax (as defined in 4.3.1), allocate the
next subdomain.
3. If the remaining components are personal-name
components, conforming to the restrictions of 4.2.2,
then EBNF.encoded-pn should be derived to form
822.local-part. In other cases the remaining
components should simply be encoded as a 822.local-part
using the EBNF.std-orname syntax. Where registered
domain defined types exist, the DD. syntax should not
be used.
4. If this step is reached for an 822-P1 recipient, then
the address is invalid. For other addresses, if the
derived 822.local-part can only be encoded by use of
822.quoted-string, the gateway may optionally use the
ASCII to 822.local-part mapping defined in Appendix A,
dependent on the mail protocols of the networks being
relayed to. Use of this encoding is discouraged.
4.3. Repeated Mappings
The mappings defined are symmetrical across a single gateway,
except in certain pathological cases (see chapter 3). However, it
is always possible to specify any valid address across a gateway.
This symmetry is particularly useful in cases of (mail exploder
type) distribution list expansion. For example, an X.400 user
sends to a list on an RFC 822 system which he belongs to. The
received message will have the originator and any 3rd party X.400
O/R names in correct format (rather than doubly encoded). In
cases (X.400 or RFC 822) where there is common agreement on
gateway identification, then this will apply to multiple gateways.
However, the syntax may be used to source route.
For example: X.400 -> RFC 822 -> X.400
C = "UK"
ADMD = "BT"
PRMD = "AC"
"JNT-Mail" = "/PN=Duval/DD.Title=Manager/(a)FR.PTT.Inria"
Kille [Page 33]
RFC 987 June 1986
Mapping between X.400 and RFC 822
This will be sent to an arbitrary UK Academic Community gateway
by X.400. Then by JNT Mail to another gateway determined by
the domain FR.PTT.Inria. This will then derive the X.400 O/R
Name:
C = "FR"
ADMD = "PTT"
PRMD = "Inria"
PN.S = "Duval"
"Title" = "Manager"
Similarly: RFC 822 -> X.400 -> RFC 822
"/C=UK/ADMD=BT/PRMD=AC/RFC-822=jj(a)seismo.css.gov/"
@monet.berkeley.edu
/C=UK/ADMD=BT/PRMD=AC/RFC-822=jj#l#a#r#seismo.css.gov/
@monet.berkeley.edu
The second case uses the Appendix A encoding to avoid
822.quoted-text. This will be sent to monet.berkeley.edu by
RFC 822, then to the AC PRMD by X.400, and then to
jj@seismo.css.gov by RFC 822.
4.4. The full P1 / 822-P1 mapping
There are two basic mappings at the P1 level:
1. 822-P1 return address <-> P1.UMPDUEnvelope.originator
2. 822-P1 recipient <-> P1.RecipientInfo
822-P1 recipients and return addresses are encoded as
EBNF.822-address. As P1.UMPDUEnvelope.originator is encoded as
P1.ORName, mapping 1) has already been specified.
P1.RecipientInfo contains a P1.ORName and additional information.
The handling of this additional information is now specified.
4.4.1. RFC 822 -> X.400
The following default settings should be made for each
component of P1.RecipientInfo.
P1.ExtensionIdentifier
This can be set systematically by the X.400 system.
Kille [Page 34]
RFC 987 June 1986
Mapping between X.400 and RFC 822
P1.RecipientInfo.perRecipientFlag
Responsibility Flag should be set. Report Request should
be set according to content return policy, as discussed
in section 5.3. User Report Request should be set to
Basic.
P1.ExplicitConversion
This optional component should be omitted.
4.4.2. X.400 -> RFC 822
The mapping only takes place in cases where
P1.RecipientInfo.perRecipientFlag Responsibility Flag is set.
The following treatment should be given to the other
P1.RecipientInfo components.
P1.ExtensionIdentifier
Not used.
P1.RecipientInfo.perRecipientFlag
If ReportRequest is Confirmed or Audit-and-Confirmed then
a delivery report indicating success should be sent by
the gateway. This report should use each
P1.ReportedRecipientInfo.SupplementaryInformation to
indicate the identity of the gateway, and the nature of
the report (i.e. only as far as the gateway). Failures
will be handled by returning RFC 822 messages, and so
User Report Request set to No report is ignored.
P1.ExplicitConversion
If present, the O/R name should be rejected, unless the
requested conversion can be achieved. None of the
currently recognised values of this parameter are
appropriate to a gateway using this specification.
Kille [Page 35]
RFC 987 June 1986
Mapping between X.400 and RFC 822
4.5. The full P2 / RFC 822 mapping
All RFC 822 addresses are assumed to use the 822.mailbox syntax.
This should include all 822.comments associated with the lexical
tokens of the 822.mailbox. All P2.ORNames are encoded within the
syntax P2.ORDescriptor, or P2.Recipient (or within Message IDs).
An asymmetrical mapping is defined between these components.
4.5.1. RFC 822 -> X.400
The following sequence is followed.
1. Take the address, and extract an EBNF.822-address.
This can be derived trivially from either the
822.addr-spec or 822.route-addr syntax. This is mapped
to P2.ORName as described above.
2. A string should be built consisting of (if present):
- The 822.phrase component if it is a 822.phrase
822.route-addr construct.
- Any 822.comments, in order, retaining the
parentheses.
This string should then be encoded into T.61 (as
described in chapter 3). If the string is not null,
it should be assigned to P2.ORDescriptor.freeformName.
3. P2.ORDescriptor.telephoneNumber should be omitted.
4. In cases of converting to P2.Recipient,
P2.Recipient.replyRequest and
P2.Recipient.reportRequest should be omitted.
If the 822.group construct is present, each included
822.mailbox should be encoded as above. The 822.group should
be mapped to T.61, and a P2.ORDesciptor with only a
freeformName component built from it.
4.5.2. X.400 -> RFC 822
In the basic case, where P2.ORName is present, proceed as
follows.
1. Encode P2.ORName as EBNF.822-address.
Kille [Page 36]
RFC 987 June 1986
Mapping between X.400 and RFC 822
2a. If P2.ORDescriptor.freeformName is present, convert it
to ASCII (chapter 3), and use use this as the
822.phrase component of 822.mailbox using the
822.phrase 822.route-addr construct.
2b. If P2.ORDescriptor.freeformName is absent, if
EBNF.822-address is parsed as 822.addr-spec use this as
the encoding of 822.mailbox. If EBNF.822-address is
parsed as 822.route 822.addr-spec, then a 822.phrase
taken from 822.local-part should be added.
3. If P2.ORDescriptor.telephoneNumber is present, this
should be placed in a trailing 822.comment.
4. If P2.Recipient.reportRequest has the
receiptNotification bit set, then an 822.comment
"(Receipt Notification Requested)" should be appended
to the address. The effort of correlating P1 and P2
information is too great to justify the gateway sending
Receipt Notifications.
5. If P2.Recipient.replyRequest is present, an 822.comment
"(Reply requested)" or "(Reply not requested)" should
be appended to the address, dependent on its value.
If P2.ORName is absent, P2.ORDescriptor.freeformName should be
converted to ASCII, and used with the RFC 822 822.group syntax:
freeformname ":" ";"
Steps 3-5 should then be followed.
4.6. Message IDs
There is a need to map both ways between 822.msg-id and
P2.IPMessageID. A mapping is defined which is symmetrical for
non-pathological cases. The mapping allows for the fact that
P2.IPMessageID.PrintableString is mandatory for the Cen/Cenelec
profile. This allows for good things to happen when messages pass
multiple times across the X.400/RFC 822 boundary. A mapping
between 822.msg-id and P1.MPDUIdentifier is defined. This allows
for X.400 error messages to reference an RFC 822 ID, which is
preferable to a gateway generated ID.
Kille [Page 37]
RFC 987 June 1986
Mapping between X.400 and RFC 822
4.6.1. P2.IPMessageID -> 822.msg-id
P2.IPMessageID.ORName is used to generate an 822.addr-spec, as
defined above. P2.IPMessageID.PrintableString is mapped to
ASCII, as defined in chapter 3. This string (if it is present
and if the value is not "RFC-822") is appended to the front of
the 822.local-part of the 822.msg-id, with "*" as a separator.
If no ORName is present, an 822.msg-id of the form
"PrintableString*@gateway-domain" is generated.
4.6.2. 822.msg-id -> P2.IPMessageID
822.local-part is parsed as:
[ printablestring "*" ] real-local-part
If EBNF.printablestring is found, it is mapped to
PrintableString, and used as P2.IPMessageID.PrintableString.
Otherwise
P2.IPMessageID.PrintableString is set to "RFC-822". This
arbitrary value allows for conformance to Cen/Cenelec. If
EBNF.real-local-part is not present, no P2.IPMessageID.ORName
is generated. Otherwise, 822.local-part is replaced with
EBNF.real-local-part, and 822.addr-spec is mapped to
P2.IPMessageID.ORName as defined above.
4.6.3. 822.msg-id -> P1.MPDUIdentifier
P1.CountryName is assigned to "", P1.AdministrationDomainName
to 822.domain (from 822.msg-id) and P1.MPDUIdentifier.IA5String
to 822.local-part (from 822.msg-id).
4.6.4. P1.MPDUIdentifier -> 822.msg-id
822.local-part is set to P1.MPDUIdentifier.IA5String, with any
CRLF mapped to SPACE. If P1.CountryName is "", 822.domain is
set to P1.AdministrationDomainName; Otherwise to
P1.AdministrationDomainName ".." P1.CountryName. If there are
any specials, the domain literal encoding should be used.
Kille [Page 38]
RFC 987 June 1986
Mapping between X.400 and RFC 822
Chapter 5 -- Protocol Elements
This chapter gives detailed mappings for the functions outlined in
chapters 1 and 2. It makes extensive use of the notations and
mappings defined in chapters 3 and 4. This chapter is structured as
follows:
5.1. Basic RFC 822 -> X.400 mappings
5.2. A definition of some new RFC 822 elements, and their mapping
to X.400.
5.3 Some special handling associated with Return of Contents.
5.4. X.400 -> RFC 822
5.1. RFC 822 -> X.400
First, the basic functions of an 822-P1 protocol should be mapped
as follows:
822-P1 Originator
Mapped to P1.UMPDUEnvelope.originator (see chapter 4).
822-P1 Recipient
Mapped to P1.RecipientInfo (see chapter 4).
The RFC 822 headers are used to generate both a P1.UMPDUEnvelope
and a P2.Heading. The IP Message will have either one or two
P2.BodyParts which will be type P2.IA5Text with no
P2.IA5Text.repertoire component. The last P2.BodyPart will contain
the RFC 822 message body. If there are any RFC 822 headers which
indicate mapping into the P2.BodyPart, then two P2.BodyParts are
generated. If a revised version of P2 allowed for extensible
header specification, this would be seen as a preferable mapping.
The first body part will start with the line:
RFC-822-Headers:
The rest of this body part will contain all of the headers not
otherwise mapped (both 822.field-name and 822.field-body). The
order of any such headers should be preserved. Similarly,
ordering within P2.Heading and P1.UMPDUEnvelope should reflect
ordering within the RFC 822 header. No P1 or P2 optional fields
are generated unless specified.
Kille [Page 39]
RFC 987 June 1986
Mapping between X.400 and RFC 822
A pro-forma X.400 message is now specified. Some of these
defaults may be changed by the values in the RFC 822 message being
mapped. The mandatory P1 and P2 components have the following
defaults.
P1.MPDUIdentifier
The default should be unique value generated by the gateway.
P1.OriginatorORName
Always generated from 822-P1.
P1.ContentType
P1.ContentType.p2
P1.RecipientInfo
These will always be supplied from 822-P1.
P1.Trace
The last P1.TraceInformation component is generated such
that: P1.TraceInformation.GlobalDomainIdentifier is set to
the local vaglue. P1.DomainSuppliedInfo.action is set to
relayed. P1.DomainSuppliedInfo.arrival is set to the current
time. P1.DomainSuppliedInfo.previous may be set if there is
anything sensible to set it to.
P2.IPMessageID
The default should be a unique value generated by the
gateway.
The following optional parameters should be set:
P1.PerMessageFlag
The P1.PerMessageFlag.contentReturnRequest bit should be set
according to the discussion in section 5.3. The
P1.PerMessageFlag.alternateRecipientAllowed bit should be
set, as it seems desirable to maximise opportunity for
(reliable) delivery.
Kille [Page 40]
RFC 987 June 1986
Mapping between X.400 and RFC 822
The RFC 822 headings should be mapped as follows:
Received:
Fudged onto P1.TraceInformation (try not to grimace too
much). P1.DomainSuppliedInfo.action is set to relayed.
P1.DomainSuppliedInfo.arrival is set to the date-time
component P1.TraceInformation.GlobalDomainIdentifier has
P1.CountryName as a null string, and
P1..AdministrationDomainName as the domain of the receiving
host (if present - null string if not).
P1.DomainSuppliedInfo.previous has P1.CountryName as a null
string, and P1.AdministrationDomainName has the domain of
the sending host with all other information enclosed in
round parentheses. The encoding of ASCII to PrintableString
(chapter 3) should be used if needed. For example:
Received: from 44e.cs.ucl.ac.uk by vax2.Cs.Ucl.AC.UK
with SMTP id a002110; 18 Dec 85 10:40 GMT
maps to -
P1.GlobalDomainIdentifier
CountryName = ""
AdministrationDomainName = "vax2.Cs.Ucl.AC.UK"
P1.DomainSuppliedInfo
arrival = 18 Dec 85 10:40 GMT
action = relayed
previous
CountryName = ""
AdministrationDomainName =
"44e.cs.ucl.ac.uk (with SMTP id a002110)"
Date:
This is used to set the first component of
P1.TraceInformation. The mandatory components are set as
follows:
P1.GlobalDomainIdentifier
CountryName = ""
AdministrationDomainName = ""
P1.DomainSuppliedInfo
arrival = time derived from Date:
action = relayed
No optional fields are used in the trace.
Kille [Page 41]
RFC 987 June 1986
Mapping between X.400 and RFC 822
Message-Id:
Mapped to P2.IPMessageID. If the RFC 822 message does not
contain a P1-Message-ID: field, the Message-Id: field is
also mapped to P1.MPDUIdentifier. For these, and all other
fields containing msg-id the mappings of chapter 4 are used
for each msg-id.
From:
If Sender: is present, this is mapped to
P2.AuthorisingUsers. If not, it is mapped to P2.Originator.
For this, and other components containing addresses, the
mappings of chapter 4 are used for each address.
Sender:
Mapped to P2.Originator.
Reply-To:
Mapped to P2.Heading.replyToUsers.
To:
Mapped to P2.Heading.primaryRecipients
Cc:
Mapped to P2.Heading.copyRecipients.
Bcc:
Mapped to P2.Heading.blindCopyRecipients.
In-Reply-To:
Mapped to P2.Heading.inReplyTo for the first (if any)
822.msg-id component. If the field contains an 822.phrase
component, or there are multiple 822.msg-id components, the
ENTIRE field is passed in the P2.BodyPart.
References:
Mapped to P2.Heading.crossReferences.
Kille [Page 42]
RFC 987 June 1986
Mapping between X.400 and RFC 822
Keywords:
Passed in the P2.BodyPart.
Subject:
Mapped to P2.Heading.subject. The field-body uses the
mapping referenced in chapter 3 from ASCII to T.61.
Comments:
Passed in the P2.BodyPart.
Encrypted:
Passed in the P2.BodyPart.
Resent-*
Passed in the P2..BodyPart <8>.
Other Fields
In particular X-* fields, and "illegal" fields in common
usage (e.g. "Fruit-of-the-day:") are passed in the
P2.BodyPart. The same treatment should be applied to
RFC 822 fields where the content of the field does not
conform to RFC 822 (e.g. a Date: field with unparsable
syntax).
5.2. Extended RFC 822 Elements -> X.400
First an EBNF definition of a number of extended fields is given,
and then a mapping to X.400 is defined. In most cases, the
RFC 822 syntax is defined to make this mapping very
straightforward, and so no detailed explanation of the mapping is
needed.
extended-field = "P1-Message-ID" ":" p1-msg-id
/ "X400-Trace" ":" x400-trace
/ "Original-Encoded-Information-Types"
":"encoded-info
/ "P1-Content-Type" ":" p1-content-type
/ "UA-Content-ID" ":" printablestring
/ "Priority" ":" priority
/ "P1-Recipient" : 1 mailbox
/ "Deferred-Delivery" ":" date-time
Kille [Page 43]
RFC 987 June 1986
Mapping between X.400 and RFC 822
/ "Bilateral-Info" ":" bilateral-info
/ "Obsoletes" ":" 1 msg-id
/ "Expiry-Date" ":" date-time
/ "Reply-By" ":" date-time
/ "Importance" ":" importance
/ "Sensitivity" ":" sensitivity
/ "Autoforwarded" ":" boolean
p1-msg-id = global-id ";" *text
p1-content-type = "P2" / atom
x400-trace = global-id ";"
"arrival" date-time
[ "deferred" date-time ]
[ "action" action ]
[ "converted" "(" encoded-info ")" ]
[ "previous" global-id ]
action = "Relayed" / "Rerouted" / escape
global-id = c "*" admd [ "*" prmd ]
encoded-info = 1 encoded-type
encoded-type = "Undefined" ; undefined (0)
/ "Telex" ; tLX (1)
/ "IA5-Text" ; iA5Text (2)
/ "G3-Fax" ; g3Fax (3)
/ "TIF0" ; tIF0 (4)
/ "Teletex" ; tTX (5)
/ "Videotex" ; videotex (6)
/ "Voice" ; voice (7)
/ "SFD" ; sFD (8)
/ "TIF1" ; tIF1 (9)
/ escape
priority = "normal" / "non-urgent" / "urgent" / escape
bilateral-info = c "*" admd "*" *text
importance = "low" / "normal" / "high" / escape
sensitivity = "Personal" / "Private"
/ "Company-Confidential" / escape
escape = 1*DIGIT
Kille [Page 44]
RFC 987 June 1986
Mapping between X.400 and RFC 822
With the exception of "Bilateral-Info:" and "X400-Trace:", there
must be no more than one of each of these fields in an RFC 822
header. Any field beginning with the String "Autoforwarded-" is
valid if the field would be syntactically valid with this string
removed.
The mappings to X.400 are as follows:
P1-Message-ID:
Mapped to P1.UMPDUEnvelope.MPDUIdentifier. This take
precedence over any value derived from Message-ID:.
X400-Trace:
Mapped to the next component of
P1.UMPDUEnvelope.Traceinformation. Care should be taken to
preserve order. If one or more of these mappings is made,
then a trace component should NOT be generated from the
Date: field which should be redundant. This is because the
message has previously come from X.400, and the Date:
information will be redundant. Note that all trace
information (Received: and "X400-Trace:") in the RFC 822
message will be in strict order, with the most recent at the
top. This order should be preserved in the mapping.
Original-Encoded-Information-Types:
This is used to set P1.UMPDUEnvelope.original.
P1.EncodedInformationTypes.[0] has bits set according to
each of the encoded-info components in this field. Any
escape values should not be encoded.
P1-Content-Type:
If the value is anything other than "P2", the mapping should
not be performed (unless the new value has some semantics to
the gateway).
UA-Content-ID:
Mapped to P1.UMPDUEnvelope.UAContentID.
Priority:
Mapped to P1.UMPDUEnvelope.Priority. An escape value should
be encoded as P1.Priority.normal.
Kille [Page 45]
RFC 987 June 1986
Mapping between X.400 and RFC 822
P1-Recipient:
If this field is set, the
P1.PerMessageFlag.discloseRecipients bit should be set. Any
of the addresses here which do not correspond to 822-P1
recipients should be added to the P1 recipient list, with
the responsibility bit turned off.
Deferred-Delivery:
Mapped to P1.UMPDUEnvelope.deferredDelivery. Note that the
value of this field should always be in the past, as this
field should only be present in messages which have come
originally from X.400. Thus there should be no implied
action. See also the comments on the reverse mapping.
Bilateral-Info:
No attempt is made to reconvert this information back to
X.400.
Obsoletes:
Mapped to P2.Heading.obsoletes.
Expiry-Date:
Mapped to P2.Heading.expiryDate.
Reply-By:
Mapped to P2.Heading.replyBy.
Importance:
Mapped to P2.Heading.importance. An escape value should be
encoded as P2.Heading.importance.normal.
Sensitivity:
Mapped to P2.Heading.sensitivity. An escape value should be
encoded as P2.Heading.sensitivity.normal.
Autoforwarded:
If this field is present and the value is "TRUE", there will
be zero or more field names beginning "Autoforwarded-".
Kille [Page 46]
RFC 987 June 1986
Mapping between X.400 and RFC 822
These should be taken, and the string "Autoforwarded-"
stripped. These fields, in conjunction with the 822-P1
information should be used to build an IP Message. Any
implied actions should be taken. P2.Heading.autoforwarded is
set in this message. The other RFC 822 fields are used to
build another IP Message, which is used as the single body
part of the first message. This mechanism does not nest.
5.3. Return of Contents
It is not clear how widely supported X.400 return of contents
service will be. However, profiling work suggests that most
systems will not support this service. As this service is
expected in the RFC 822 world, two approaches are specified (it is
not so necessary in the X.400 world, as delivery reports are
distinguished from messages). The choice will depend on the
service level of the X.400 community being serviced by the
gateway.
In environments where return of contents is widely supported, the
P1.PerMessageFlag content return request bit will be set, and the
Report Request bit in P1.PerRecipientFlag will be set to
Confirmed, for every message passing from RFC 822 -> X.400. The
content return service can then be passed back to the end
(RFC 822) user in a straightforward manner.
In environments where return of contents is not widely supported,
a gateway must make special provisions to handle return of
contents. For every message passing from RFC 822 -> X.400, the
P1.PerMessageFlag content return request bit will be set, and the
Report Request bit in P1.PerRecipientFlag will be set to
Confirmed. When the delivery report comes back, the gateway can
note that the message has been delivered to the recipient(s) in
question. If a non-delivery report is received, a meaningful
report (containing some or all of the original message) can be
sent to the 822-P1 originator. If no report is received for a
recipient, a (timeout) failure notice should be sent to the 822-P1
originator. The gateway may retransmit the X.400 message if it
wishes. Delivery confirmations should only be sent back to the
822-P1 originator if the P1.PerRecipientFlag User Report Request
bit is set to Confirmed.
Kille [Page 47]
RFC 987 June 1986
Mapping between X.400 and RFC 822
5.4. X.400 -> RFC 822
5.4.1. General
This section describes how to build a pro-forma message, and
then explains how these defaults may be overridden. It should
be noted that RFC 822 folding of headers should be used in an
appropriate manner.
5.4.2. Service MPDU
5.4.2.1. Probe
Any P1.ProbeMPDU should be serviced by the gateway, as there
is no equivalent RFC 822 functionality. The value of the
reply is dependent on whether the gateway could service a
User MPDU with the values specified in the probe. The reply
should make use of P1.SupplementaryInformation to indicate
that the probe was serviced by the gateway.
5.4.2.2. Delivery Report
The 822-P1 components are constructed as follows:
822-P1 Originator
This is set to an 822.addr-spec pointing to an
administrator at the gateway.
822-P1 Recipient
The single recipient is constructed from
P1.DeliveryReportEnvelope.originator, using the
mappings of chapter 4.
The mandatory RFC 822 headers for an RFC 822 pro-forma are
constructed as follows:
Date:
From the P1.DomainSuppliedInfo.arrival component of
the first P1.TraceInformation component.
From:
This is set to the same as the 822-P1 originator. An
Kille [Page 48]
RFC 987 June 1986
Mapping between X.400 and RFC 822
appropriate phrase component may be added (e.g. giving
the name of the gateway).
To:
The same as the 822-P1 recipient.
A Subject: field should be added, which contains some
appropriate words (e.g. "Delivery Report").
The other two P1.DeliveryReportEnvelope parameters should be
mapped as follows:
P1.DeliveryReportEnvelope.report
This should be mapped to a P1-Message-Id: field.
P1.DeliveryReportEnvelope.TraceInformation
Each component should be mapped to an "X400-Trace:"
field. RFC 822 and X.400 ordering should be
maintained (see 5.3).
The P1.DeliveryReportContent parameters should be mapped to
a series of new RFC 822 headers. These new headers are
intended for processing in the RFC 822 world. No attempt
will be made to reverse the mappings.
drc-field = "Delivery-Report-Content-Original"
":" msg-id
/ "Delivery-Report-Content-Intermediate-Trace"
":" x400-trace
/ "Delivery-Report-Content-UA-Content-ID"
":" printablestring
/ "Delivery-Report-Content-Billing-Information"
":" *text
/ "Delivery-Report-Content-Reported-Recipient-Info"
":" drc-info
drc-info = mailbox ";"
last-trace ";"
"ext" 1*DIGIT
"flags" 2DIGIT
[ "intended" mailbox ] ";"
[ "info" printablestring ]
Kille [Page 49]
RFC 987 June 1986
Mapping between X.400 and RFC 822
last-trace = drc-report ";"
date-time ";"
[ "converted" "(" encoded-info ")"
drc-report = "SUCCESS" drc-success
/ "FAILURE" drc-failure
drc-success = date-time ";" 1*DIGIT
drc-failure = *text [ ";" *text ] ";"
There may be multiple
"Delivery-Report-Content-Intermediate-Trace:" and
"Delivery-Report-Content-Reported-Recipient-Info:" fields.
The msg-id for "Delivery-Report-Content-Original" is derived
according to the mapping of chapter 4. EBNF.drc-failure may
use numeric values or textual explanation. The latter is
preferred. All P1.DeliveryReportContent parameters are
mapped to the corresponding component. The order of
"Delivery-Report-Content-Intermediate-Trace:" should have
the most recently stamped one first.
The body of the RFC 822 message should be a human readable
description of the critical parts of the
P1.DeliveryReportContent. In particular, the failed
recipients, and failure reason should be given. Some or all
of the original message should be included in the delivery
report. The original message will be available at the
gateway, as discussed in section 5.3.
5.4.3. User MPDU
These elements are the basis for both Status Report and IP
Message.
The 822-P1 components are constructed as follows:
822-P1 Originator
This is derived from P1.UMPDUEnvelope.originator.
822-P1 Recipient
Each recipient is constructed from the P1.RecipientInfo,
as described in chapter 4. This describes actions as
well as format mappings.
Kille [Page 50]
RFC 987 June 1986
Mapping between X.400 and RFC 822
The mandatory RFC 822 field pro-forma is derived as follows.
In most cases where the P1.UMPDUContent is an IP Message, these
defaults will be overridden:
Date:
From the P1.DomainSuppliedInfo.arrival component of the
first P1.TraceInformation component.
From:
From the P1.UMPDUEnvelope.originator, as defined in
chapter 4.
To:
This default is only required if the generated RFC 822
message has no destination specification. If
P1.PerMessageFlag.discloseRecipients is set then it
should contain the ORName in each P1.RecipientInfo
component. If it is not set, the it should be set to
"To: No Recipients Specified : ;".
The mappings, and any actions for each P1.UserMPDU element is
now considered.
P1.MPDUIdentifier
Mapped to the extended RFC 822 field "P1-Message-ID:".
Note that the sequence CRLF is mapped to SPACE, which
makes the mapping irreversible for such cases.
P1.UMPDUEnvelope.original
Mapped to the extended RFC 822 field
"Original-Encoded-Information-Types:". If it contains
only P2.IA5Text, the RFC 822 field may be omitted.
P1.ContentType
As this can currently only have one value, it is not
mapped, on the basis that it is redundant. If the field
contains any value other than P2, then the UMPDU should
be rejected.
Kille [Page 51]
RFC 987 June 1986
Mapping between X.400 and RFC 822
P1.UAContentID
Mapped to the extended RFC 822 field "UA-Content-Id:".
P1.Priority
Mapped to the extended RFC 822 field "Priority:".
P1.PerMesageFlag
This has a number of components:
- discloseRecipients
If this bit is set, a "P1-Recipient:" field should
be generated, and contain each of the P1
recipients.
- conversionProhibited
If this bit is set, the message should be rejected
if it contains P2.BodyPart which is not P2.IA5Text
or P2.ForwardedIPMessage.
- alternateRecipientAllowed
The value of this bit is ignored.
- contentReturnRequest
The value of this bit is ignored.
P1.UMPDUEnvelope.deferredDelivery
This should be mapped to the extended RFC 822 field
"Deferred-Delivery:". X.400 profiles, and in particular
the CEN/CENELEC profile [CEN/CENELEC/85a], specify that
this element must be supported at the first MTA. Thus,
it is expected that the value of this element will always
be in the past. If it is not, the function may
optionally be implemented by the gateway: that is, the
gateway should hold the message until the time specified
in the protocol element. Thus the extended RFC 822 field
is just for information.
Kille [Page 52]
RFC 987 June 1986
Mapping between X.400 and RFC 822
P1.PerDomainBilateralInformation
Each component should be encoded in the extended RFC 822
field "Bilateral-Info:". P1.BilateralInfo should be
mapped into ASCII in a manner appropriate to its
contents. This submapping is not reversible.
P1.TraceInformation
This should be mapped to "X400-Trace:", as for the
delivery report.
5.4.4. Status Report
The entire status report is mapped into the body of the RFC 822
message, in the same manner as for a Delivery Report. An
appropriate "Subject:" field should be generated. As status
reports cannot be requested from the RFC 822 world, the mapping
is not likely to be used a great deal.
5.4.5. IP Message
The P1.UMPDUEnvelope pro-forma specification ensures all the
822-P1 information, and a minimal (legal) RFC 822 message. The
mappings and actions for the P2.Heading components are now
described. Basically, these are interpreted as actions and/or
mappings into RFC 822 fields. The following mappings are
specified:
P2.IPMessageID
This is mapped to the field "Message-ID:", according to
section 4.
P2.Heading.originator
If P2.Heading.authorisingUsers is present this is mapped
to Sender:, if not to From:.
P2.Heading.authorisingUsers
Mapped to From:.
P2.Heading.primaryRecipients
Mapped to To:.
Kille [Page 53]
RFC 987 June 1986
Mapping between X.400 and RFC 822
P2.Heading.copyRecipients
Mapped to Cc:.
P2.Heading.blindCopyRecipients
Mapped to Bcc:.
P2.Heading.inReplyTo
Mapped to In-Reply-To:.
P2.Heading.obsoletes
Mapped to the extended RFC 822 field "Obsoletes:"
P2.Heading.crossReferences
Mapped to References:.
P2.Heading.subject
Mapped to subject. The contents are converted to ASCII
(as defined in chapter 3). Any CRLF are not mapped, but
are used as points at which the subject field must be
folded. line.
P2.Heading.expiryDate
Mapped to the extended RFC 822 field "Expiry-Date:".
P2.Heading.replyBy
Mapped to the extended RFC 822 field "Reply-By:".
P2.Heading.replyToUsers
Mapped to Reply-To:.
P2.Heading.importance
Mapped to the extended RFC 822 field "Importance:".
P2.Heading.sensitivity
Mapped to the extended RFC 822 field "Sensitivity:".
Kille [Page 54]
RFC 987 June 1986
Mapping between X.400 and RFC 822
P2.Heading.autoforwarded
If it is set to FALSE, it is simply mapped to the
extended RFC 822 field "Autoforwarded:". If this is set
to TRUE, the P2.Body does not consist of a single
P2.ForwardedIPMessage, then there is an X.400 error, and
the message should be bounced. Otherwise the following
steps are taken.
1. The mappings for all of the message, except the
body part are completed.
2. Prepend each RFC 822 fieldname with the string
"Autoforwarded-". Mapped to the extended RFC 822
field "Autoforwarded:".
3. Add the field "Autoforwarded:" with value TRUE.
4. Convert the syntax of the P2.ForwardedIPMessage to
generate the remaining RFC 822 fields.
The P2.Body is mapped into the RFC 822 message body. Each
P2.BodyPart is converted to ASCII. If the P2.Body contains a
P2.BodyPart not listed here, the entire message should be
rejected. If there are exactly two P2.IA5Text body parts, and
the first line of the first is "RFC-822-Headers:", then the
rest of this first body part should be treated as additional
header information for the RFC 822 message. If there is an
"In-Reply-To:" field, this should be used to replace any
generated In-Reply-To: field.
In other cases of multiple P2.BodyPart, the mapping defined by
Rose and Stefferud in [Rose85b], should be used to separate the
P2.BodyParts in the single RFC 822 message body.
Individual body parts are mapped as follows:
P2.IA5Text
The mapping is trivial.
P2.TTX
If any P1.Teletex.NonBasicParams are set, the message
should be rejected. Otherwise, it should be converted to
ASCII according to chapter 3.
Kille [Page 55]
RFC 987 June 1986
Mapping between X.400 and RFC 822
P2.SFD
An SFD should be converted to ASCII as if it was being
rendered on an 79 column ASCII only VDU. It seems likely
that many gateways will not support this conversion. In
these cases, the message should be rejected.
P2.ForwardedIPMessage
The P2.ForwardedIPMessage.delivery and
P2.ForwardedIPMessage.DeliveryInformation are
discarded <9>. The IM-UAPDU should have its syntax
mapped (recursively) according to this gatewaying
specification. Clearly, it makes no sense to apply any
of the actions defined here.
Kille [Page 56]
RFC 987 June 1986
Mapping between X.400 and RFC 822
Appendix A -- Quoted String Encodings
This Appendix describes a quoting mechanism which may be used to
allow general interworking between RFC 822, and variants of RFC 822
which do not support 822.quoted-string. This is important, as the
basic X.400 <-> RFC 822 mapping makes use of 822.quoted-string.
1. ASCII <-> 822.atom
The following EBNF is specified.
atom-encoded = *( a-char / a-encoded-char )
a-char =
a-encoded-char = "_" ; (space)
/ "#u#" ; (_)
/ "#l#" ; <(>
/ "#r#" ; <)>
/ "#m#" ; (,)
/ "#c#" ; (:)
/ "#b#" ; (\)
/ "#h#" ; (#)
/ "#e#" ; ($=)
/ "#s#" ; ($/)
/ "#" 3DIGIT "#"
NOTE: There are two encodings of double characters. This is so
that systems using this encoding, do not also need to know about
the "$" quoting mechanism defined in chapter 4.
The 822.3DIGIT in EBNF.a-encoded-char must have range 0-127
(Decimal), and is interpreted in decimal as the corresponding
ASCII character. The choice of special abbreviations (as opposed
to octal encoding) provided is based on the manner in which this
mapping is most frequently used: encoding PrintableString
components of O/R names as atom. Therefore, there are special
encodings for each of the PrintableString characters not in
EBNF.a-char, except ".". Space is given a single character
encoding, due to its (expected) frequency of use, and backslash as
the RFC 822 single quote character.
To encode (ASCII -> atom): all EBNF.a-char are used directly and
all other CHAR are encoded as EBNF.a-encoded-char. To decode
(822.atom -> ASCII): if 822.atom can be parsed as
EBNF.encoded-atom reverse the previous mapping. If it cannot be
so parsed, map the characters directly.
Kille [Page 57]
RFC 987 June 1986
Mapping between X.400 and RFC 822
2. 822.local-part <-> ASCII
A related transformation is for 822.local-part (or other element
defined as '822.word ("." 822.word)') where not 822.quoted-text is
used. To encode (ASCII -> 822.local-part), all EBNF.a-char and
"." are used directly and all other 822.CHAR are encoded as
EBNF.a-encoded-char. To decode (822.local-part -> ASCII), first
attempt to parse 822.local-part as '822.atom *("." 822.atom)'. If
this fails, or if each 822.atom cannot be parsed as
EBNF.atom-encoded then map each character directly. Otherwise map
each "." directly, and each atom as in the previous section.
There are places where it is needed to convert between
PrintableString or IA5Text (X.400), and 822.word (RFC 822). word
may be encoded as 822.atom (which has a restricted character set)
or as 822.quoted-string, which can handle all ASCII characters.
If 822.quoted-string is used, clearly the mappings for
PrintableString defined in Chapter 3 provide a straightforward
mapping. However, some RFC 822 based networks cannot handle the
822.quoted-string format in all cases. This Appendix is for use
in these cases. The major requirement for this mapping is the
UNIX world, but it may well be needed in other places.
These mappings are somewhat artificial, and their usage is
discouraged, except in cases where there is no alternative.
Kille [Page 58]
RFC 987 June 1986
Mapping between X.400 and RFC 822
Appendix B -- Mappings Specific to JNT Mail
This Appendix is specific to the JNT Mail Protocol. It describes
specific changes in the context of this protocol. Addressing is not
discussed here, as it is covered in Appendix A.
1. Introduction
There are four aspects of a gateway which are JNT Mail Specific,
in addition to those relating to addressing. These are each given
a section of this appendix.
2. Acknowledge-To:
This field has no direct functional equivalent in X.400. However,
it can be supported to an extent, and can be used to improve X.400
support.
When going from JNT Mail to X.400, the User Report Request bits of
each P1.RecipientInfo.perRecipientFlag should be set to confirmed.
If there is more that one address in the Acknowledge-To: field, or
if the one address is not equivalent to the 822-P1 return address,
then:
a. Acknowledgement(s) should be generated by the gateway.
The text of these acknowledgements should indicate that
they are generated by the gateway.
b. The Acknowledge-To: field should also be passed in the
first P2.BodyPart.
When going from X.400 to JNT Mail, in cases where
P1.RecipientInfo.perRecipientFlag has the user bits set to
confirmed the copy of the message to that recipient should have an
Acknowledge-To: field containing the P.UMPDUEnvelope.originator.
No attempt should be made to map Receipt notification requests
onto Acknowledge-To:. This is because no association can be
guaranteed between P2 and P1 level addressing information.
3. Trace
JNT Mail trace uses the Via: syntax. When going from JNT Mail to
X.400, the following mapping onto P1.TraceInformation is used.
P1.DomainSuppliedInfo.action is set to relayed.
P1.DomainSuppliedInfo.arrival is set to the date-time component
Kille [Page 59]
RFC 987 June 1986
Mapping between X.400 and RFC 822
of the Via: field. P1.DomainSuppliedInfo.previous has
P1.CountryName as a null string, and
P1.AdministrationDomainName as the domain specified in the Via:
field.
P1.TraceInformation.GlobalDomainIdentifier has P1.CountryName
as a null string, and P1.AdministrationDomainName as any
commented information in the Via: field. For example:
Via: UK.AC.Edinburgh ; 17 Jun 85 9:15:29 BST (EMAS V7)
maps to -
P1.GlobalDomainIdentifier
CountryName = ""
AdministrationDomainName = "(EMAS V7)"
P1.DomainSuppliedInfo
arrival = 17 Jun 85 9:15:29 BST
action = relayed
previous
CountryName = ""
AdministrationDomainName = "UK.AC.Edinburgh"
4. Timezone specification
The extended syntax of zone defined in the JNT Mail Protocol
should be used in the mapping of UTCTime defined in chapter 3.
5. Lack of separate 822-P1 originator specification
In JNT Mail the default mapping of the P1.MPDUEnvelope.originator
is to the Sender: field. This can cause a problem if the mapping
of P2.Heading has already generated a Sender: field. To overcome
this, new extended JNT Mail field is defined. This is chosen to
align with the JNT recommendation for interworking with full
RFC 822 systems [Kille84b].
original-sender = "Original-Sender" ":" mailbox
If an IPM has no P2.heading.authorisingUsers component and
P2.Heading.originator.ORName is different from
P1.UMPDUEnvelope.originator, map P1.MPDUEnvelope.originator onto
the Sender: field.
If an IPM has a P2.heading.authorisingUsers component, and
P2.Heading.originator.ORName is different from
P1.UMPDUEnvelope.originator, P1.MPDUEnvelpoe.originator should be
Kille [Page 60]
RFC 987 June 1986
Mapping between X.400 and RFC 822
mapped onto the Sender: field, and P2.Heading.originator mapped
onto the Original-Sender: field.
In other cases the P1.MPDUEnvelope.Originator is already correctly
represented.
Note that in some pathological cases, this mapping is
asymmetrical.
Kille [Page 61]
RFC 987 June 1986
Mapping between X.400 and RFC 822
Appendix C -- Mappings Specific to Internet Mail
The Simple Mail Transfer Protocol [Postel82a] is used in the
ARPA-Internet, and in any network following the US DoD standards for
internetwork protocols. This appendix is specific to those hosts
which use SMTP to exchange mail.
1. Mapping between O/R names and SMTP addresses
The mappings of Chapter 4 are to be used.
2. Use of the ARPA Domain System
Whenever possible, domain-qualified addresses should be be used to
specify encoded O/R names. These domain encodings naturally
should be independent of any routing information.
3. Identification of gateways
The ARPA-Internet Network Information Center (NIC) will maintain a
list of registered X.400 gateways in the ARPA Internet.
Kille [Page 62]
RFC 987 June 1986
Mapping between X.400 and RFC 822
Appendix D -- Mappings Specific to Phonenet Mail
There are currently no mappings specific to Phonenet Mail.
Kille [Page 63]
RFC 987 June 1986
Mapping between X.400 and RFC 822
Appendix E -- Mappings Specific to UUCP Mail
Gatewaying of UUCP and X.400 is handled by first gatewaying the UUCP
address into RFC 822 syntax (using RFC 976) [Horton86a] and then
gatewaying the resulting RFC 822 address into X.400. For example, an
X.400 address
Country US
Organization Xerox
Personal Name John Smith
might be expressed from UUCP as
inthop!gate!gatehost.COM!/C=US/O=Xerox/PN=John.Smith/
(assuming gate is a UUCP-ARPA gateway and gatehost.COM is an
ARPA-X.400 gateway) or
inthop!gate!Xerox.COM!John.Smith
(assuming that Xerox.COM and /C=US/O=Xerox/ are equivalent.)
In the other direction, a UUCP address Smith@ATT.COM, integrated into
822, would be handled as any other 822 address. A non-integrated
address such as inthop!dest!user might be handled thought a pair of
gateways:
Country US
ADMD ATT
PRMD ARPA
Organization GateOrg
RFC-822 inthop!dest!user@gatehost.COM
or through a single X.400 to UUCP gateway:
Country US
ADMD ATT
PRMD UUCP
Organization GateOrg
UUCP inthop!dest!user
Kille [Page 64]
RFC 987 June 1986
Mapping between X.400 and RFC 822
Appendix F -- Format of Address Mapping Tables
There is a need to specify the association between the domain and
X.400 namespaces described in 4.2.1. This is defined as a table
syntax, but the syntax is defined in a manner which makes it suitable
for use with domain nameservers (such as the DARPA Domain nameservers
or the UK NRS). The symmetry of the mapping is not clear, so a
separate table is specified for each direction. For domain -> X.400:
domain-syntax "#" dmn-orname "#"
For example:
AC.UK#PRMD$DES.ADMD$BT.C$UK#
XEROX.COM#O$Xerox.ADMD$ATT.C$US#
For X.400 -> domain:
dmn-orname "#" domain-syntax "#"
EBNF.domain-syntax will be interpreted according to RFC 920.
EBNF.dmn-orname will have components ordered as defined in section
4.2.1, and with the most significant component on the RHS.
Kille [Page 65]
RFC 987 June 1986
Mapping between X.400 and RFC 822
References
Bonacker85a.
K.H. Bonacker, U. Pankoke-Babatz, and H. Santo, "EAN - Conformity
to X.400 and DFN-Pflichtenheft," GMD (Gesellschaft fur Mathematik
und Datenverarbeitung) report, June 1985.
CCITT84a.
CCITT SG 5/VII, "Recommendations X.400," Message Handling Systems:
System Model - Service Elements, October 1984.
CCITT84b.
CCITT SG 5/VII, "Recommendations X.411," Message Handling Systems:
Message Transfer Layer, October 1984.
CCITT84c.
CCITT SG 5/VII, "Recommendations X.420," Message Handling Systems:
Interpersonal Messaging User Agent Layer, October 1984.
CCITT84d.
CCITT SG 5/VII, "Recommendations X.409," Message Handling Systems:
Presentation Transfer Syntax and Notation, October 1984.
CEN/CENELEC/85a.
CEN/CENELEC/Information Technology/Working Group on Private
Message Handling Systems, "FUNCTIONAL STANDARD A/3222,"
CEN/CLC/IT/WG/PMHS N 17, October 1985.
Crocker82a.
D.H. Crocker, "Standard of the Format of ARPA Internet Text
Messages," RFC 822, August 1982.
Horton85a.
M.R. Horton, "Draft Standard for ARPA/MHS Addressing Gateways,"
AT&T Bell Laboratories, October 1985.
Kille [Page 66]
RFC 987 June 1986
Mapping between X.400 and RFC 822
Horton86a.
M.R. Horton, "UUCP Mail Interchange Format Standard", RFC 976,
February 1986.
ICL84a.
ICL, "Comparison of service elements of Grey Book Mail and X.400,"
Mailgroup Note 18: Extract from unpublished report for ITSU
(Information Technology Standards Unit), July 1984.
Kille84a.
S.E. Kille, (editor), JNT Mail Protocol (revision 1.0), Joint
Network Team, Rutherford Appleton Laboratory, March 1984.
Kille84b.
S.E. Kille, "Gatewaying between RFC 822 and JNT Mail," JNT
Mailgroup Note 15, May 1984.
Kille86a.
S.E. Kille, "O/R Names in the UK Academic Community," UK Working
Document, March 1986.
Larmouth83a.
J. Larmouth, "JNT Name Registration Technical Guide," Salford
University Computer Centre, April 1983.
Neufeld85a.
G. Neufeld, J. Demco, B. Hilpert, and R. Sample, "EAN: an X.400
message system," in Second International Symposium on Computer
Message Systems, Washington, pp. 1-13, North Holland,
September 1985.
Postel82a.
J. Postel, "Simple Mail Transfer Protocol," RFC 821, August 1982.
Postel84a.
J. Postel and J. Reynolds, "Domain Requirements," RFC 920,
October 1984.
Kille [Page 67]
RFC 987 June 1986
Mapping between X.400 and RFC 822
Rose85a.
M.T. Rose, "Mapping Service Elements between ARPA and MHS," Draft
proposal, October 1985.
Rose85b.
M.T. Rose and E.A. Stefferud, "Proposed Standard for Message
Encapsulation," RFC 934, January 1985.
Kille [Page 68]
RFC 987 June 1986
Mapping between X.400 and RFC 822
Notes:
<0> UNIX is a trademark of Bell Laboratories.
<1> The term gateway is used to describe a component performing the
protocol mappings between RFC 822 and X.400. This is standard
usage amongst mail implementors, but should be noted carefully
by transport and network service implementors. (Sometime called
a "mail relay".)
<2> If the remote protocol is JNT Mail, a notification may also be
sent by the recipient UA.
<3> The asymmetry occurs where an ASCII string contains the sequence
EBNF.ps-encoded-char. This would be mapped directly to
PrintableString, but the reverse mapping would be to the value
implied by the sequence.
<4> It might be suggested that for reasons of elegance,
EBNF.ps-delim (left parenthesis) is encoded as
EBNF.ps-encoded-char. This is not done, as it it would never be
possible to represent a PrintableString containing the character
"(" in ASCII. This is because an "(" in ASCII would be mapped
to the encoding in PrintableString.
<5> In practice, a gateway will need to parse various illegal
variants on 822.date-time. In cases where 822.date-time cannot
be parsed, it is recommended that the derived UTCTime is set to
the value at the time of translation.
<6> P2.ORname is defined as P1.ORName.
<7> This recommendation may change in the light of CCITT or
CEN/CENELEC guidelines on the use of initials.
<8> It would be possible to use a ForwardedIPMessage for these
fields, but the semantics are (arguably) slightly different, and
it is probably not worth the effort.
<9> Although this violates chapter 1, part 4, principles 2 and 3, it
is suggested that this is justified by principle 1.
Kille [Page 69]
RFC, FYI, BCP