element = service "." definition *( "." definition )
service = "IPMS" / "MTS" / "MTA"
definition = identifier / context
identifier = ALPHA *< ALPHA or DIGIT or "-" >
context = "[" 1*DIGIT "]"
The EBNF.service keys are shorthand for the following service
specifications:
IPMS IPMSInformationObjects defined in Annex E of X.420 / ISO
10021-7.
MTS MTSAbstractService defined in Section 9 of X.411 / ISO
10021-4.
MTA MTAAbstractService defined in Section 13 of X.411 / ISO
10021-4.
The first EBNF.identifier identifies a type or value key in the
context of the defined service specification. Subsequent
EBNF.identifiers identify a value label or type in the context of the
first identifier (SET or SEQUENCE). EBNF.context indicates a context
tag, and is used where there is no label or type to uniquely identify
a component. The special EBNF.identifier keyword "value" is used to
denote an element of a sequence.
For example, IPMS.Heading.subject defines the subject element of the
IPMS heading. The same syntax is also used to refer to element
values. For example, MTS.EncodedInformationTypes.[0].g3Fax refers to
a value of MTS.EncodedInformationTypes.[0].
3.2. ASCII and IA5
A gateway will interpret all IA5 as ASCII. Thus, mapping between
these forms is conceptual.
3.3. Standard Types
There is a need to convert between ASCII text, and some of the types
defined in ASN.1 [CCITT/ISO88d]. For each case, an EBNF syntax
definition is given, for use in all of this specification, which
leads to a mapping between ASN.1, and an EBNF construct.
All EBNF syntax definitions of ASN.1 types are in lower case, whereas
ASN.1 types 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-restricted-char = 1DIGIT / 1ALPHA / " " / "'" / "+"
/ "," / "-" / "." / "/" / ":" / "=" / "?"
ps-delim = "(" / ")"
ps-char = ps-delim / ps-restricted-char
This can be used to represent real printable strings in EBNF.
3.3.4. T.61String
In cases where T.61 strings are only used for conveying human
interpreted information, the aim of a mapping should be to render the
characters appropriately in the remote character set, rather than to
maximise reversibility. For these cases, the mappings to IA5 defined
in CCITT Recommendation X.408 (1988) should be used [CCITT/ISO88a].
These will then be encoded in ASCII.
There is also a need to represent Teletex Strings in ASCII, for some
aspects of O/R Address. For these, the following encoding is used:
teletex-string = *( ps-char / t61-encoded )
t61-encoded = "{" 1* t61-encoded-char "}"
t61-encoded-char = 3DIGIT
Common characters are mapped simply. Other octets are mapped using a
quoting mechanism similar to the printable string mechanism. Each
octet is represented as 3 decimal digits.
There are a number of places where a string may have a Teletex and/or
Printable String representation. The following BNF is used to
represent this.
teletex-and-or-ps = [ printablestring ] [ "*" teletex-string ]
The natural mapping is restricted to EBNF.ps-char, in order to make
the full BNF easier to parse.
3.3.5. UTCTime
Both UTCTime and the RFC822 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.
Note:
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.
The UTCTime format which specifies the timezone offset should be
used.
3.3.6. Integer
A basic ASN.1 Integer will be mapped onto EBNF.numericstring. In many
cases ASN.1 will enumerate Integer values or use ENUMERATED. An EBNF
encoding labelled-integer is provided. When mapping from EBNF to
ASN.1, only the integer value is mapped, and the associated text is
discarded. When mapping from ASN.1 to EBNF, addition of an
appropriate text label is strongly encouraged.
labelled-integer ::= [ key-string ] "(" numericstring ")"
key-string = *key-char
key-char = <a-z, A-Z, 1-9, and "-">
3.3.7. Object Identifier
Object identifiers are represented in a form similar to that
given in ASN.1. The numbers are mandatory, to ease encoding.
It is recommended that as many strings as possible are used, to
facilitate user recognition.
object-identifier ::= [ defined-value ] oid-comp-list
oid-comp-list ::= oid-comp oid-comp-list
| oid-comp
defined-value ::= key-string
oid-comp ::= [ key-string ] "(" numericstring ")"
3.4. Encoding ASCII in Printable String
Some information in RFC822 is represented in ASCII, and needs to be
mapped into X.400 elements encoded as printable string. For this
reason, a mechanism to represent ASCII encoded as PrintableString is
needed.
A structured subset of EBNF.printablestring is now defined. This can
be used to encode ASCII in the PrintableString character set.
ps-encoded = *( ps-restricted-char / ps-encoded-char )
ps-encoded-char = "(a)" ; (@)
/ "(p)" ; (%)
/ "(b)" ; (!)
/ "(q)" ; (")
/ "(u)" ; (_)
/ "(l)" ; "("
/ "(r)" ; ")"
/ "(" 3DIGIT ")"
The 822.3DIGIT in EBNF.ps-encoded-char must have range 0-127, and is
interpreted in decimal as the corresponding ASCII character. Special
encodings are given for: at sign (@), percent (%), exclamation
mark/bang (!), double quote ("), underscore (_), left bracket ((),
and right bracket ()). These characters, with the exception of round
brackets, are not included in PrintableString, but are common in RFC
822 addresses. The abbreviations will ease specification of RFC822
addresses from an X.400 system. These special encodings should be
mapped in a case insensitive manner, but always be generated in lower
case.
A reversible mapping between PrintableString and ASCII can now be
defined. The reversibility means that some values of printable
string (containing round braces) cannot be generated from ASCII.
Therefore, this mapping must only be used in cases where the
printable strings may only be derived from ASCII (and will therefore
have a restricted domain). For example, in this specification, it is
only applied to a Domain defined attribute which will have been
generated by use of this specification and a value such as "(" would
not be possible.
To encode ASCII as PrintableString, the EBNF.ps-encoded syntax is
used, with all EBNF.ps-restricted-char mapped directly. All other
822.CHAR are encoded as EBNF.ps-encoded-char.
To encode PrintableString as ASCII, parse PrintableString as
EBNF.ps-encoded, and then reverse the previous mapping. If the
PrintableString cannot be parsed, then the mapping is being applied
in to an inappropriate value, and an error should be given to the
procedure doing the mapping. In some cases, it may be preferable to
pass the printable string through unaltered.
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) <-> @
(l)a(r) <-> (a)
(126) <-> ~
( -> (
(l) <-> (
Chapter 4 -- Addressing
Addressing is probably the trickiest problem of an X.400 <-> RFC822
gateway. Therefore it is given a separate chapter. This chapter, as
a side effect, also defines a textual representation of an X.400 O/R
Address.
Initially, we consider an address in the (human) mail user sense of
"what is typed at the mailsystem to reference a mail user". A basic
RFC822 address is defined by the EBNF EBNF.822-address:
822-address = [ route ] addr-spec
In an 822-MTS protocol, the originator and each recipient should be
considered to be defined by such a construct. In an RFC822 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 O/R Address, used by the MTS for routing, is defined
by MTS.ORAddress. In IPMS, the MTS.ORAddress is encapsulated within
IPMS.ORDescriptor.
It can be seen that RFC822 822.address must be mapped with
IPMS.ORDescriptor, and that RFC822 EBNF.822-address must be mapped
with MTS.ORAddress.
4.1. A textual representation of MTS.ORAddress
MTS.ORAddress is structured as a set of attribute value pairs. It is
clearly necessary to be able to encode this in ASCII for gatewaying
purposes. All aspects should be encoded, in order to guarantee
return of error messages, and to optimise third party replies.
4.2. Basic Representation
An O/R Address has a number of structured and unstructured
attributes. For each unstructured attribute, a key and an encoding
is specified. For structured attributes, the X.400 attribute is
mapped onto one or more attribute value pairs. For domain defined
attributes, each element of the sequence will be mapped onto a triple
(key and two values), with each value having the same encoding. The
attributes are as follows, with 1984 attributes given in the first
part of the table. For each attribute, a reference is given,
consisting of the relevant sections in X.402 / ISO 10021-2, and the
extension identifier for 88 only attributes:
Attribute (Component) Key Enc Ref Id
84/88 Attributes
MTS.CountryName C P 18.3.3
MTS.AdministrationDomainName ADMD P 18.3.1
MTS.PrivateDomainName PRMD P 18.3.21
MTS.NetworkAddress X121 N 18.3.7
MTS.TerminalIdentifier T-ID N 18.3.23
MTS.OrganizationName O P/T 18.3.9
MTS.OrganizationalUnitNames.value OU P/T 18.3.10
MTS.NumericUserIdentifier UA-ID N 18.3.8
MTS.PersonalName PN P/T 18.3.12
MTS.PersonalName.surname S P/T 18.3.12
MTS.PersonalName.given-name G P/T 18.3.12
MTS.PersonalName.initials I P/T 18.3.12
MTS.PersonalName
.generation-qualifier GQ P/T 18.3.12
MTS.DomainDefinedAttribute.value DD P/T 18.1
88 Attributes
MTS.CommonName CN P/T 18.3.2 1
MTS.TeletexCommonName CN P/T 18.3.2 2
MTS.TeletexOrganizationName O P/T 18.3.9 3
MTS.TeletexPersonalName PN P/T 18.3.12 4
MTS.TeletexPersonalName.surname S P/T 18.3.12 4
MTS.TeletexPersonalName.given-name G P/T 18.3.12 4
MTS.TeletexPersonalName.initials I P/T 18.3.12 4
MTS.TeletexPersonalName
.generation-qualifier GQ P/T 18.3.12 4
MTS.TeletexOrganizationalUnitNames
.value OU P/T 18.3.10 5
MTS.TeletexDomainDefinedAttribute
.value DD P/T 18.1 6
MTS.PDSName PD-SYSTEM P 18.3.11 7
MTS.PhysicalDeliveryCountryName PD-C P 18.3.13 8
MTS.PostalCode POSTCODE P 18.3.19 9
MTS.PhysicalDeliveryOfficeName PD-OFFICE P/T 18.3.14 10
MTS.PhysicalDeliveryOfficeNumber PD-OFFICE-NUM P/T 18.3.15 11
MTS.ExtensionORAddressComponents PD-EXT-D P/T 18.3.4 12
MTS.PhysicalDeliveryPersonName PD-PN P/T 18.3.17 13
MTS.PhysicalDelivery PD-O P/T 18.3.16 14
OrganizationName
MTS.ExtensionPhysicalDelivery
AddressComponents PD-EXT-LOC P/T 18.3.5 15
MTS.UnformattedPostalAddress PD-ADDRESS P/T 18.3.25 16
MTS.StreetAddress STREET P/T 18.3.22 17
MTS.PostOfficeBoxAddress PO-BOX P/T 18.3.18 18
MTS.PosteRestanteAddress POSTE-RESTANTE P/T 18.3.20 19
MTS.UniquePostalName PD-UNIQUE P/T 18.3.26 20
MTS.LocalPostalAttributes PD-LOCAL P/T 18.3.6 21
MTS.ExtendedNetworkAddress
.e163-4-address.number NET-NUM N 18.3.7 22
MTS.ExtendedNetworkAddress
.e163-4-address.sub-address NET-SUB N 18.3.7 22
MTS.ExtendedNetworkAddress
.psap-address NET-PSAP X 18.3.7 22
MTS.TerminalType NET-TTYPE I 18.3.24 23
The following keys identify different EBNF encodings, which are
associated with the ASCII representation of MTS.ORAddress.
Key Encoding
P printablestring
N numericstring
T teletex-string
P/T teletex-and-or-ps
I labelled-integer
X presentation-address
The BNF for presentation-address is taken from the specification "A
String Encoding of Presentation Address" [Kille89a].
In most cases, the EBNF encoding maps directly to the ASN.1 encoding
of the attribute. There are a few exceptions. In cases where an
attribute can be encoded as either a PrintableString or NumericString
(Country, ADMD, PRMD), either form should be mapped into the BNF.
When generating ASN.1, the NumericString encoding should be used if
the string contains only digits.
There are a number of cases where the P/T (teletex-and-or-ps)
representation is used. Where the key maps to a single attribute,
this choice is reflected in the encoding of the attribute (attributes
10-21). For most of the 1984 attributes and common name, there is a
printablestring and a teletex variant. This pair of attributes is
mapped onto the single component here. This will give a clean
mapping for the common cases where only one form of the name is used.
4.2.1. Encoding of Personal Name
Handling of Personal Name and Teletex 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 defined, which is designed to provide
a clean encoding for the common cases of O/R address specification
where:
1. There is no generational qualifier
2. Initials contain only letters
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.
The following EBNF is defined:
encoded-pn = [ given "." ] *( initial "." ) surname
given = 2*<ps-char not including ".">
initial = ALPHA
surname = printablestring
This can be used to map from any string containing only printable
string characters to an O/R address personal name. Parse the string
according to the EBNF. The given name and surname are assigned
directly. All EBNF.initial tokens are concatenated without
intervening full stops to generate the initials.
For an O/R address which follows the above restrictions, a string can
be derived in the natural manner. In this case, the mapping will be
reversible.
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 X.400 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!
4.2.2. Standard Encoding of MTS.ORAddress
Given this structure, we can specify a BNF representation of an O/R
Address.
std-or-address = 1*( "/" attribute "=" value ) "/"
attribute = standard-type
/ "RFC-822"
/ registered-dd-type
/ dd-key "." std-printablestring
standard-type = key-string
registered-dd-type
= key-string
dd-key = key-string
value = std-printablestring
std-printablestring
= *( std-char / std-pair )
std-char = <"{", "}", "*", and any ps-char
except "/" and "=">
std-pair = "$" ps-char
The standard-type is any key defined in the table in Section 4.2,
except PN, and DD. The value, after quote removal, should be
interpreted according to the defined encoding.
If the standard-type is PN, the value is interpreted according to
EBNF.encoded-pn, and the components of MTS.PersonalName and/or
MTS.TeletexPersonalName derived accordingly.
If dd-key is the recognised Domain Defined string (DD), then the type
and value should be interpreted according to the syntax implied from
the encoding, and aligned to either the teletex or printable string
form. Key and value should have the same encoding.
If value is "RFC-822", then the (printable string) Domain Defined
Type of "RFC-822" is assumed. This is an optimised encoding of the
domain defined type defined by this specification.
The matching of all keywords should be done in a case- independent
manner.
If the value is registered-dd-type, the value is registered with the
IANA and will be listed in the Assigned Numbers RFC, then the value
should be interpreted accordingly. This restriction maximises the
syntax checking which can be done at a gateway.
4.3. EBNF.822-address <-> MTS.ORAddress
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 RFC822
worlds, which would be needed for this to work.
Therefore, an asymmetrical mapping is defined, which can be
symmetrical where there is appropriate administrative control.
4.3.1. X.400 encoded in RFC822
The std-or-address syntax is used to encode O/R Address information
in the 822.local-part of EBNF.822-address. Further O/R Address
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 Addresses. The only way to
encode the full PrintableString character set in a domain is by use
of the 822.domain-ref syntax (i.e., 822.atom). This is likely to
cause problems on many systems. The effective character set of
domains is in practice reduced from the RFC822 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 RFC822 world, and
will not be interpreted by the gateway (although they may have
identified the gateway from within the RFC822 world).
This form of source routing is now discouraged in the Internet
(Host Requirements, page 58 [Braden89a]).
The 822.domain associated with the 822.local-part may also identify
the gateway from within the RFC822 world. This final 822.domain may
be used to determine some number of O/R Address attributes. The
following O/R Address 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
There may be multiple Organisational Units.
Associations may be defined between domain specifications, and
some set of attributes. This association proceeds hierarchically.
For example, if a domain implies ADMD, it also implies country.
Subdomains under this are associated according to the O/R Address
hierarchy. For example:
=> "AC.UK" might be associated with
C="GB", ADMD="GOLD 400", PRMD="UK.AC"
then domain "R-D.Salford.AC.UK" maps with
C="GB", ADMD="GOLD 400", PRMD="UK.AC", O="Salford", OU="R-D"
There are three 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 = alphanum [ *alphanumhyphen alphanum ]
alphanum = <ALPHA or DIGIT>
alphanumhyphen = <ALPHA or DIGIT or HYPHEN>
Although RFC822 allows for a more general syntax, this
restricted syntax is chosen as it is the one chosen by the
various domain service administrations.
3. To deal with missing elements in the hierarchy. A domain
may be associated with an omitted attribute in conjunction
with several present ones. When performing the algorithmic
insertion of components lower in the hierarchy, the omitted
value should be skipped. For example, if "HNE.EGM" is
associated with "C=TC", "ADMD=ECQ", "PRMD=HNE", and omitted
organisation, then "ZI.HNE.EGM" is mapped with "C=TC",
"ADMD=ECQ", "PRMD=HNE", "OU=ZI". It should be noted that
attributes may have null values, and that this is treated
separately from omitted attributes (whilst it would be bad
practice to treat these two cases differently, they must be
allowed for).
This set of mappings need only be known by the gateways relaying
between the RFC822 world, and the O/R Address space 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.
The remaining attributes are encoded on the LHS, using the EBNF.std-
or-address syntax. For example:
/I=J/S=Linnimouth/GQ=5/@Marketing.Widget.COM
encodes the MTS.ORAddress consisting of:
MTS.CountryName = "TC"
MTS.AdministrationDomainName = "BTT"
MTS.OrganizationName = "Widget"
MTS.OrganizationalUnitNames.value = "Marketing"
MTS.PersonalName.surname = "Linnimouth"
MTS.PersonalName.initials = "J"
MTS.PersonalName.generation-qualifier = "5"
The first three attributes are determined by the domain Widget.COM.
Then, the first element of OrganizationalUnitNames is determined
systematically, and the remaining attributes are encoded on the LHS.
In an extreme case, all of the attributes will be on the LHS. As the
domain cannot be null, the RHS will simply be a domain indicating the
gateway.
The RHS (domain) encoding is designed to deal cleanly with common
addresses, and so the amount of information on the RHS should be
maximised. In particular, it covers the Mnemonic O/R Address using a
1984 compatible encoding. This is seen as the dominant form of O/R
Address. Use of other forms of O/R Address, and teletex encoded
attributes will require an LHS encoding.
There is a further mechanism to simplify the encoding of common
cases, where the only attributes to be encoded on the LHS is a (non-
Teletex) Personal Name attributes which comply with the restrictions
of 4.2.1. To achieve this, the 822.local-part shall be encoded as
EBNF.encoded-pn. In the previous example, if the GenerationQualifier
was not present, the encoding J.Linnimouth@Marketing.Widget.COM would
result.
From the standpoint of the RFC822 Message Transfer System, the
domain specification is simply used to route the message in the
standard manner. The standard domain mechanisms are are used to
select appropriate gateways for the corresponding O/R Address space.
In most cases, this will be done by registering the higher levels,
and assuming that the gateway can handle the lower levels.
4.3.2. RFC822 encoded in X.400
In some cases, the encoding defined above may be reversed, to give a
"natural" encoding of genuine RFC822 addresses. This depends
largely on the allocation of appropriate management domains.
The general case is mapped by use of domain defined attributes. A
Domain defined type "RFC-822" is defined. The associated attribute
value is an ASCII string encoded according to Section 3.3.3 of this
specification. The interpretation of the ASCII string depends on the
context of the gateway.
1. In the context of RFC822, and RFC1034
[Crocker82a, Mockapetris87a], the string can be used
directly.
2. In the context of the JNT Mail protocol, and the NRS
[Kille84a, Larmouth83a], the string should be interpreted
according to Mailgroup Note 15 [Kille84b].
3. In the context of UUCP based systems, the string should be
interpreted as defined in [Horton86a].
Other O/R Address attributes will be used to identify a context in
which the O/R Address will be interpreted. This might be a
Management Domain, or some part of a Management Domain which
identifies a gateway MTA. For example:
C = "GB"
ADMD = "GOLD 400"
PRMD = "UK.AC"
O = "UCL"
OU = "CS"
"RFC-822" = "Jimmy(a)WIDGET-LABS.CO.UK"
OR
C = "TC"
ADMD = "Wizz.mail"
PRMD = "42"
"rfc-822" = "Postel(a)venera.isi.edu"
Note in each case the PrintableString encoding of "@" as "(a)". In
the second example, the "RFC-822" domain defined attribute is
interpreted everywhere within the (Private) Management Domain. In
the first 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.
4.3.3. Component Ordering
In most cases, ordering of O/R Address components is not significant
for the mappings specified. However, Organisational Units (printable
string and teletex forms) and Domain Defined Attributes are specified
as SEQUENCE in MTS.ORAddress, and so their order may be significant.
This specification needs to take account of this:
1. To allow consistent mapping into the domain hierarchy
2. To ensure preservation of order over multiple mappings.
There are three places where an order must be specified:
1. The text encoding (std-or-address) of MTS.ORAddress as used
in the local-part of an RFC822 address. An order is needed
for those components which may have multiple values
(Organisational Unit, and Domain Defined Attributes). When
generating an 822.std-or-address, components of a given type
shall be in hierarchical order with the most significant
component on the RHS. If there is an Organisation
Attribute, it shall be to the right of any Organisational
Unit attributes. These requirements are for the following
reasons:
- Alignment to the hierarchy of other components in RFC
822 addresses (thus, Organisational Units will appear
in the same order, whether encoded on the RHS or LHS).
Note the differences of JNT Mail as described in
Appendix B.
- Backwards compatibility with RFC987/1026.
- To ensure that gateways generate consistent addresses.
This is both to help end users, and to generate
identical message ids.
Further, it is recommended that all other attributes are
generated according to this ordering, so that all attributes
so encoded follow a consistent hierarchy.
There will be some cases where an X.400 O/R address of this
encoding will be generated by an end user from external
information. The ordering of attributes may be inverted or
mixed. For this reason, the following heuristics may be
applied:
- If there is an Organisation attribute to the left of
any Org Unit attribute, assume that the hierarchy is
inverted.
- If an inversion of the Org Unit hierarchy generates a
valid address, when the preferred order does not,
assume that the hierarchy is inverted.
2. For the Organisational Units (OU) in MTS.ORAddress, the
first OU in the SEQUENCE is the most significant, as
specified in X.400.
3. For the Domain Defined Attributes in MTS.ORAddress, the
First Domain Defined Attribute in the SEQUENCE is the most
significant.
Note that although this ordering is mandatory for this
mapping, there are NO implications on ordering significance
within X.400, where this is a Management Domain issue.
4.3.4. RFC822 -> X.400
There are two basic cases:
1. X.400 addresses encoded in RFC822. This will also include
RFC822 addresses which are given reversible encodings.
2. "Genuine" RFC822 addresses.
The mapping should proceed as follows, by first assuming case 1).
STAGE I.
1. If the 822-address is not of the form:
local-part "@" domain
Go to stage II.
NOTE:It may be appropriate to reduce a source route address
to this form by removal of all bar the last domain. In
terms of the design intentions of RFC822, this would
be an incorrect action. However, in most real cases,
it will do the "right" thing and provide a better
service to the end user. This is a reflection on the
excessive and inappropriate use of source routing in
RFC822 based systems. Either approach, or the
intermediate approach of stripping only domain
references which reference the local gateway are
conformant to this specification.
2. Attempt to parse EBNF.domain as:
*( domain-syntax "." ) known-domain
Where EBNF.known-domain is the longest possible match in a
list of supported mappings (see Appendix F). If this fails,
and the EBNF.domain does not explicitly identify the local
gateway, go to stage II. If it succeeds, allocate the
attributes associated with EBNF.known-domain, and
systematically allocate the attributes implied by each
EBNF.domain-syntax component. If the domain explicitly
identifies the gateway, allocate no attributes.
3. If the local-part contains any characters not in
PrintableString, go to stage II.
4. If the 822.local-part uses the 822.quoted-string encoding,
remove this quoting. Parse the (unquoted) 822.local-part
according to the EBNF EBNF.std-or-address. If this parse
fails, parse the local-part according to the EBNF
EBNF.encoded-pn. The result is a set of type/value pairs.
If the values generated conflict with those derived in step
2 (e.g., a duplicated country attribute), the domain should
be assumed to be an RFC987 gateway. In this case, take
only the LHS derived attributes. Otherwise add LHS and RHS
derived attributes together.
5. Associate the EBNF.attribute-value syntax (determined from
the identified type) with each value, and check that it
conforms. If not, go to stage II.
6. Ensure that the set of attributes conforms both to the
MTS.ORAddress specification and to the restrictions on this
set given in X.400. If not go to stage II.
7. Build the O/R Address from this information.
STAGE II.
This will only be reached if the RFC822 EBNF.822-address is not
a valid X.400 encoding. If the address is an 822-MTS recipient
address, it must be rejected, as there is a need to interpret
such an address in X.400. For the 822-MTS return address, and
any addresses in the RFC822 header, they should now be encoded
as RFC822 addresses in an X.400 O/R Name:
1. Convert the EBNF.822-address to PrintableString, as
specified in Chapter 3.
2. The "RFC-822" domain defined attribute should be generated
from this string.
3. Build the rest of the O/R Address in the local Management
Domain agreed manner, so that the O/R Address will receive a
correct global interpretation.
Note that the domain defined attribute value has a maximum length
of MTS.ub-domain-defined-attribute-value-length (128). If this
is exceeded by a mapping at the MTS level, then the gateway
should reject the message in question. If this occurs at the
IPMS level, then the action should depend on the policy being
taken, which is discussed in Section 5.1.3.
4.3.5. X.400 -> RFC822
There are two basic cases:
1. RFC822 addresses encoded in X.400.
2. "Genuine" X.400 addresses. This may include symmetrically
encoded RFC822 addresses.
When a MTS Recipient O/R Address is interpreted, gatewaying will be
selected if there a single "RFC-822" domain defined attribute
present. In this case, use mapping A. For other O/R Addresses
which:
1. Contain the special attribute.
AND
2. Identifies the local gateway or any other known gateway with
the other attributes.
Use mapping A. In other cases, use mapping B.
NOTE:
A pragmatic approach would be to assume that any O/R
Address with the special domain defined attribute identifies
an RFC822 address. This will usually work correctly, but is
in principle not correct.
Mapping A
1. Map the domain defined attribute value to ASCII, as defined
in Chapter 3.
Mapping B
This will be used for X.400 addresses which do not use the explicit
RFC822 encoding.
1. For all string encoded attributes, remove any leading or
trailing spaces, and replace adjacent spaces with a single
space.
2. 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 the domain as
the domain specification of the local gateway, and go to
step 4.
3. Following the 4.3.1 hierarchy and noting any omitted
components implied by the mapping tables (see Appendix F),
if each successive component exists, and conforms to the
syntax EBNF.domain-syntax (as defined in 4.3.1), allocate
the next subdomain. At least one attribute of the X.400
address should not be mapped onto subdomain, as
822.local-part cannot be null.
4. If the remaining components are personal-name components,
conforming to the restrictions of 4.2.1, 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-or-address syntax. If
necessary, the 822.quoted-string encoding should be used.
If the derived 822.local-part can only be encoded by use of
822.quoted-string, then use of the mapping defined
in [Kille89b] may be appropriate. Use of this mapping is
discouraged.
4.4. Repeated Mappings
The mappings defined are symmetrical and reversible across a single
gateway. The 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 RFC822 system which he belongs to. The
received message will have the originator and any 3rd party X.400 O/R
Addresses in correct format (rather than doubly encoded). In cases
(X.400 or RFC822) where there is common agreement on gateway
identification, then this will apply to multiple gateways.
When a message traverses multiple gateways, the mapping will always
be reversible, in that a reply can be generated which will correctly
reverse the path. In many cases, the mapping will also be
symmetrical, which will appear clean to the end user. For example,
if countries "AB" and "XY" have RFC822 networks, but are
interconnected by X.400, the following may happen: The originator
specifies:
Joe.Soap@Widget.PTT.XY
This is routed to a gateway, which generates:
C = "XY"
ADMD = "PTT"
PRMD = "Griddle MHS Providers"
Organisation = "Widget Corporation"
Surname = "Soap"
Given Name = "Joe"
This is then routed to another gateway where the mapping is reversed
to give:
Joe.Soap@Widget.PTT.XY
Here, use of the gateway is transparent.
Mappings will only be symmetrical where mapping tables are defined.
In other cases, the reversibility is more important, due to the (far
too frequent) cases where RFC822 and X.400 services are partitioned.
The syntax may be used to source route. THIS IS STRONGLY
DISCOURAGED. For example:
X.400 -> RFC822 -> X.400
C = "UK"
ADMD = "Gold 400"
PRMD = "UK.AC"
"RFC-822" = "/PN=Duval/DD.Title=Manager/(a)Inria.ATLAS.FR"
This will be sent to an arbitrary UK Academic Community gateway by
X.400. Then it will be sent by JNT Mail to another gateway
determined by the domain Inria.ATLAS.FR (FR.ATLAS.Inria). This will
then derive the X.400 O/R Address:
C = "FR"
ADMD = "ATLAS"
PRMD = "Inria"
PN.S = "Duval"
"Title" = "Manager"
Similarly:
RFC822 -> X.400 -> RFC822
"/C=UK/ADMD=BT/PRMD=AC/RFC-822=jj(a)seismo.css.gov/"
@monet.berkeley.edu
This will be sent to monet.berkeley.edu by RFC822, then to the AC
PRMD by X.400, and then to jj@seismo.css.gov by RFC822.
4.5. Directory Names
Directory Names are an optional part of O/R Name, along with O/R
Address. The RFC822 addresses are mapped onto the O/R Address
component. As there is no functional mapping for the Directory Name
on the RFC822 side, a textual mapping should be used. There is no
requirement for reversibility in terms of the goals of this
specification. There may be some loss of functionality in terms of
third party recipients where only a directory name is given, but this
seems preferable to the significant extra complexity of adding a full
mapping for Directory Names.
4.6. MTS Mappings
The basic mappings at the MTS level are:
1) 822-MTS originator ->
MTS.PerMessageSubmissionFields.originator-name
MTS.OtherMessageDeliveryFields.originator-name ->
822-MTS originator
2) 822-MTS recipient ->
MTS.PerRecipientMessageSubmissionFields
MTS.OtherMessageDeliveryFields.this-recipient-name ->
822-MTS recipient
822-MTS recipients and return addresses are encoded as EBNF.822-
address.
The MTS Originator is always encoded as MTS.OriginatorName, which
maps onto MTS.ORAddressAndOptionalDirectoryName, which in turn maps
onto MTS.ORName.
4.6.1. RFC822 -> X.400
From the 822-MTS Originator, use the basic ORAddress mapping, to
generate MTS.PerMessageSubmissionFields.originator-name (MTS.ORName),
without a DirectoryName.
For recipients, the following settings should be made for each
component of MTS.PerRecipientMessageSubmissionFields.
recipient-name
This should be derived from the 822-MTS recipient by the
basic ORAddress mapping.
originator-report-request
This should be set according to content return policy, as
discussed in Section 5.2.
explicit-conversion
This optional component should be omitted, as this service
is not needed.
extensions
The default value (no extensions) should be used.
4.6.2. X.400 -> RFC822
The basic functionality is to generate the 822-MTS originator and
recipients. There is information present on the X.400 side, which
cannot be mapped into analogous 822-MTS services. For this reason,
new RFC822 fields are added for the MTS Originator and Recipients.
The information discarded at the 822-MTS level should be present in
these fields. There may also be the need to generate a delivery
report.
4.6.2.1. 822-MTS Mappings
Use the basic ORAddress mapping, to generate the 822-MTS originator
(return address) from MTS.OtherMessageDeliveryFields.originator-name
(MTS.ORName). If MTS.ORName.directory-name is present, it should be
discarded.
The 822-MTS recipient is conceptually generated from
MTS.OtherMessageDeliveryFields.this-recipient-name. This is done by
taking MTS.OtherMessageDeliveryFields.this-recipient-name, and
generating an 822-MTS recipient according to the basic ORAddress
mapping, discarding MTS.ORName.directory-name if present. However,
if this model was followed exactly, there would be no possibility to
have multiple 822-MTS recipients on a single message. This is
unacceptable, and so layering is violated. The mapping needs to use
the MTA level information, and map each value of
MTA.PerRecipientMessageTransferFields.recipient-name, where the
responsibility bit is set, onto an 822-MTS recipient.
4.6.2.2. Generation of RFC822 Headers
Not all per-recipient information can be passed at the 822-MTS level.
For this reason, two new RFC822 headers are created, in order to
carry this information to the RFC822 recipient. These fields are
"X400-Originator:" and "X400-Recipients:".
The "X400-Originator:" field should be set to the same value as the
822-MTS originator. In addition, if
MTS.OtherMessageDeliveryFields.originator-name (MTS.ORName) contains
MTS.ORName.directory-name then this Directory Name should be
represented in an 822.comment.
Recipient names, taken from each value of
MTS.OtherMessageDeliveryFields.this-recipient-name and
MTS.OtherMessageDeliveryFields.other-recipient-names should be made
available to the RFC822 user by use of the "X400-Recipients:" field.
By taking the recipients at the MTS level, disclosure of recipients
will be dealt with correctly. If any MTS.ORName.directory-name is
present, it should be represented in an 822.comment. If
MTS.OtherMessageDeliveryFields.orignally-intended-recipient-name is
present, then it should be represented in an associated 822.comment,
starting with the string "Originally Intended Recipient".
In addition, the following per-recipient services from
MTS.OtherMessageDeliveryFields.extensions should be represented in
comments if they are used. None of these services can be provided on
RFC822 networks, and so in general these will be informative strings
associated with other MTS recipients. In some cases, string values
are defined. For the remainder, the string value may be chosen by
the implementor. If the parameter has a default value, then no
comment should be inserted.
requested-delivery-method
physical-forwarding-prohibited
"(Physical Forwarding Prohibited)".
physical-forwarding-address-request
"(Physical Forwarding Address Requested)".
physical-delivery-modes
registered-mail-type
recipient-number-for-advice
physical-rendition-attributes
physical-delivery-report-request
"(Physical Delivery Report Requested)".
proof-of-delivery-request
"(Proof of Delivery Requested)".
4.6.2.3. Delivery Report Generation
If MTA.PerRecipientMessageTransferFields.per-recipient-indicators
requires a positive delivery notification, this should be
generated by the gateway. Supplementary Information should be
set to indicate that the report is gateway generated.
4.6.3. Message IDs (MTS)
A mapping from 822.msg-id to MTS.MTSIdentifier is defined. The
reverse mapping is not needed, as MTS.MTSIdentifier is always
mapped onto new RFC822 fields. The value of
MTS.MTSIdentifier.local-part will facilitate correlation of
gateway errors.
To map from 822.msg-id, apply the standard mapping to
822.msg-id, in order to generate an MTS.ORAddress. The Country,
ADMD, and PRMD components of this should be used to generate
MTS.MTSIdentifier.global-domain-identifier.
MTS.MTSIdentifier.local-identifier should be set to the
822.msg-id, including the braces "<" and ">". If this string is
longer than MTS.ub-local-id-length (32), then it should be
truncated to this length.
The reverse mapping is not used in this specification. It
would be applicable where MTS.MTSIdentifier.local-identifier is
of syntax 822.msg-id, and it algorithmically identifies
MTS.MTSIdentifier.
4.7. IPMS Mappings
All RFC822 addresses are assumed to use the 822.mailbox syntax.