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Network Working Group H. Lachman
INTERNET-DRAFT Netscape Communications Corp.
Intended Category: Standards Track May 1999
Expires: November 1999
Filename: draft-lachman-laser-ldap-mail-routing-00.txt
LDAP Schema for Intranet Mail Routing
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
This draft is being discussed on the Laser mailing list at
<laser@sunroof.eng.sun.com>. Subscription requests can be sent to
<laser-request@sunroof.eng.sun.com> (send an email message with the
word "subscribe" in the body). More information on the mailing list
along with an archive of back messages is available at
<http://playground.sun.com/laser/>.
Copyright Notice
Copyright (C) The Internet Society (1999). All Rights Reserved.
Abstract
This document defines an LDAP [1] object class called
'inetLocalMailRecipient' and associated attributes that provide a way
to designate an LDAP entry as one that represents a local (intra-
organizational) email recipient, to specify the recipient's email
address(es), and to provide routing information pertinent to the
Lachman [Page 1]
INTERNET-DRAFT LDAP Schema for Intranet Mail Routing May 1999
recipient. This is intended to support SMTP [2] message transfer
agents in routing RFC 822-based email [3] within a private enterprise
only, and is not to be used in the process of routing email across
the public Internet.
1. Background and Motivation
LDAP-based directory services are currently being used in many
organizations as a repository of information about users and other
network entities (such as groups of users, network resources, etc.).
In cases where LDAP entries are used to represent entities that are
email recipients (e.g., a mail user or a mailing list), the LDAP
entries provide a convenient place to store per-recipient data, such
as a recipient's email address.
In many organizations, an email recipient may have an email address
(e.g., "joe@example.com") that does not specify the host that
receives mail for that recipient (e.g., "host42.example.com"). A
message transfer agent (MTA) responsible for routing mail within the
organization needs some way to determine the appropriate target host
for such a recipient. A common solution is the sendmail "aliases"
database which may contain a record that provides the necessary per-
recipient routing information (e.g., "joe: joe@host42"). A drawback
of this solution is that if the organization hosts more than one DNS
domain (e.g., "example.com" and "example.org", with "joe" in each
domain being different recipients), a more explicit mapping is
desirable. The schema defined in this document provides a way to
represent such mappings in LDAP and X.500 [4] directory services.
An LDAP entry that represents an email recipient could conceivably
contain a variety of attributes related to email, such as disk quota
and delivery preferences. We consider here only attributes that
specify address information and routing information; these attributes
may be useful to multiple MTAs within the organization since one or
more MTAs may be responsible for intra-organizational routing. The
various MTAs in an organization may have been developed by different
implementors, so a common schema is desirable for such attributes.
2. Overview
The 'inetLocalMailRecipient' object class and associated attributes
identify an LDAP entry as representing an SMTP mail recipient (in the
sense "recipient" is used in RFC 821). A recipient may be a mail
user, a mailing list, an auto-responder of some kind (e.g., a mailing
list subscription program), a network device such as a printer or fax
machine, or other recipient type. Address attributes and routing
attributes are provided to aid SMTP MTAs in routing mail within an
organization to the appropriate target MTA for each recipient.
Lachman [Page 2]
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Once on the target MTA, a message is handled as per the recipient
type and options (which may be specified using other auxiliary object
classes and is outside the scope of this document). For example, the
message may be delivered to a user mailbox, or to a program or
network device, and/or forwarded to another recipient. Or, the
target MTA may be a gateway to a non-SMTP mail routing and delivery
system including non-SMTP MTAs. Note that, in this discussion,
"target MTA" refers to the final SMTP destination of messages for the
recipient in question, as we are considering routing of mail only
among the SMTP MTAs within an organization.
Routing of mail between different organizations across the public
Internet is outside the scope of this document, as the mechanism for
this is already standardized [5,6]. An 'inetLocalMailRecipient'
entry represents a mail recipient that is local to the organization
in question, not recipients in other organizations. This means that
the domain names that appear within the 'mail',
'mailAlternateAddress', 'mailHost', and 'mailRoutingAddress'
attribute values in an 'inetLocalMailRecipient' entry must be DNS
domain names that are within the administrative authority of the
organization in question (i.e., the organization within which MTAs
are accessing such entries and using these attributes for mail
routing).
LDAP entries that are not 'inetLocalMailRecipient' entries should be
ignored by MTAs for the purpose of routing. Such entries may contain
a 'mail' attribute since this attribute is used in other object
classes. An example is a conference room whose LDAP entry contains
contact information (e.g., email address and telephone number) for
the person who books reservations for the room; the conference room
is not a mail recipient, and can safely be ignored by MTAs doing
route determination based on recipient address.
3. Object Class and Attribute Definitions
The 'inetLocalMailRecipient' object class and associated attributes
are defined (using syntaxes given in [7]) as follows.
3.1 The inetLocalMailRecipient Object Class
( 2.16.840.1.113730.3.2.[[TBD]]
NAME 'inetLocalMailRecipient'
SUP top
AUXILIARY
MAY ( mail $ mailAlternateAddress $
mailHost $ mailRoutingAddress
)
)
Lachman [Page 3]
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The 'inetLocalMailRecipient' object class signifies that the entry
represents an entity within the organization that can receive SMTP
mail, such as a mail user or a mailing list.
3.2 Address Attributes
( 0.9.2342.19200300.100.1.3
NAME 'mail'
DESC 'RFC 822 email address of this recipient'
EQUALITY caseIgnoreIA5Match
SYNTAX '1.3.6.1.4.1.1466.115.121.1.26{256}'
)
The attribute name 'mail' is a synonym for 'rfc822Mailbox', as
defined earlier in [8]. This attribute specifies the recipient's
"primary" or "advertised" email address, i.e., that which might
appear on a business card; for example, "user@example.com". The
address conforms to the syntax of an 'addr-spec' as defined in RFC
822.
( 2.16.840.1.113730.3.1.13
NAME 'mailAlternateAddress'
DESC 'alternate RFC 822 email address of this recipient'
EQUALITY caseIgnoreIA5Match
SYNTAX '1.3.6.1.4.1.1466.115.121.1.26{256}'
)
The 'mailAlternateAddress' attribute is used to specify alternate
email addresses, if any, for the recipient; for example,
"nickname@example.com". The address conforms to the syntax of an
'addr-spec' as defined in RFC 822.
When determining the disposition of a given message, an MTA may
search the directory for an entry with object class
'inetLocalMailRecipient' and a 'mail' or 'mailAlternateAddress'
attribute matching the message's recipient address. If exactly one
matching entry is found, the MTA may regard the message as being
addressed to the entity that is represented by the directory entry.
The 'mailAlternateAddress' attribute may also be used to represent a
"wildcard domain" address, e.g., "@example.org", meaning that if mail
arrives for "someone@example.org", and there is no recipient with
that address specified as 'mail' or 'mailAlternateAddress', then the
recipient with the wildcard domain address should receive the mail.
In short, address attributes may be used by an LDAP entry to answer
the question "what is/are this account's email address(es)?"
Lachman [Page 4]
INTERNET-DRAFT LDAP Schema for Intranet Mail Routing May 1999
3.3 Routing Attributes
( 2.16.840.1.113730.3.1.18
NAME 'mailHost'
DESC 'fully-qualified hostname of the MTA that is the final
SMTP destination of messages to this recipient'
EQUALITY caseIgnoreIA5Match
SYNTAX '1.3.6.1.4.1.1466.115.121.1.26{256}'
SINGLE-VALUE
)
The 'mailHost' attribute indicates which SMTP MTA considers the
recipient's mail to be locally handlable. This information can be
used for routing, in that an intermediary MTA may take it to be the
destination for messages addressed to this recipient. The hostname
is specified as a fully-qualified DNS hostname with no trailing dot
(e.g., "host42.example.com").
( 2.16.840.1.113730.3.1.47
NAME 'mailRoutingAddress'
DESC 'RFC 822 address to use when routing messages to
the SMTP MTA of this recipient'
EQUALITY caseIgnoreIA5Match
SYNTAX '1.3.6.1.4.1.1466.115.121.1.26{256}'
SINGLE-VALUE
)
The 'mailRoutingAddress' attribute indicates a routing address for
the recipient. The address conforms to the syntax of an 'addr-spec'
in RFC 822. An intermediary MTA may use this information to route
the message to the MTA that handles mail for this recipient. This is
useful in cases where, for a given recipient, the target MTA prefers
a particular address to appear as the recipient address in the SMTP
envelope. So, 'mailRoutingAddress' may be used as an alternative to
'mailHost', and is intended to have the same effect as 'mailHost'
except that 'mailRoutingAddress' suggests an address for rewriting
the envelope. With 'mailHost', the envelope address either is not
rewritten, or is rewritten according to implementation-specific rules
and/or configuration.
If both 'mailHost' and 'mailRoutingAddress' are present, the
suggested interpretation is that messages are to be routed to the
host indicated by 'mailHost', while rewriting the envelope as per
'mailRoutingAddress'. In theory, there could be peculiar cases where
this is necessary, but this is not normally expected.
Absense of both 'mailHost' and 'mailRoutingAddress' should be
considered an error, unless "location-independent" recipient types
Lachman [Page 5]
INTERNET-DRAFT LDAP Schema for Intranet Mail Routing May 1999
are supported by the various MTAs within the organization. This
would allow any MTA in the organization to handle the processing of
mail for, say, a mailing list. This presumes that the various MTAs
all recognize the recipient type in question, suggesting a need to
standardize recipient types that could be "location-independent".
In short, routing attributes may be used by an LDAP entry to answer
the question "how should MTAs route mail to this account?"
(analogous to using the sendmail "aliases" database for per-user
routing within an organization). This is in contrast with
"forwarding"; forwarding and delivery options may be specified in an
LDAP entry to answer the question "what happens to mail once it
arrives at this account?", which may include forwarding to some other
account within or outside the organization (analogous to using the
sendmail ".forward" file). Such options are outside the scope of the
'inetLocalMailRecipient' schema definition.
4. Examples
The following examples illustrate possible uses of the
'inetLocalMailRecipient' object class.
Here is an example of an LDAP entry representing a mail user:
dn: uid=joe,o=Example Corp,c=US
objectclass: top
objectclass: person
objectclass: organizationalPerson
objectclass: inetOrgPerson
objectclass: inetLocalMailRecipient
objectclass: nsMessagingServerUser
cn: Joe User
sn: User
uid: joe
userpassword: {crypt}y2KxtbzMYnApU
mail: joe@example.com
mailhost: nsmail1.example.com
maildeliveryoption: mailbox
mailquota: 1000000
mailforwardingaddress: mary@example.com
Joe User is a user of a hypothetical mail system called NS Messaging.
Let's say mail arrives on an MTA called "mx.example.com", addressed
to "joe@example.com". The MTA searches the directory for a mail
recipient with that address, using an LDAP search filter [9] such as:
(&(objectClass=inetLocalMailRecipient)
(|(mail=joe@example.com)
Lachman [Page 6]
INTERNET-DRAFT LDAP Schema for Intranet Mail Routing May 1999
(mailAlternateAddress=joe@example.com)))
It finds Joe's LDAP entry, and routes the message to the target MTA
"nsmail1.example.com", while not rewriting the SMTP envelope
recipient address. Then, "nsmail1.example.com" receives the message,
searches for and finds the recipient in the directory, ascertains
that it is the recipient's target MTA, and handles the message as per
other attributes in the recipient's entry and/or the MTA
configuration (in this case, the message is delivered to a mailbox,
and forwarded to another recipient).
Note that this document does not specify what search filters are to
be used by MTAs (although the one above is recommended), nor does it
specify the rules an MTA is to use to ascertain whether or not it is
the target MTA for a given recipient (it could check the recipient's
'mailHost' value against its own hostname, or check the recipient's
'mailRoutingAddress', or check the MTA configuration, or some
combination of these), nor does it specify how and when MTAs should
rewrite envelopes (it may depend on the MTA configuration).
Here is another example of an LDAP entry representing a mail user:
dn: uid=john,o=Example Corp,c=US
objectclass: top
objectclass: person
objectclass: organizationalPerson
objectclass: inetOrgPerson
objectclass: inetLocalMailRecipient
objectclass: xyzMailUser
cn: John Doe
sn: Doe
uid: john
userpassword: {crypt}y2KxtbzMYnApU
mail: john@example.com
mailroutingaddress: John_Doe@xyz-gw.example.com
xyzpostofficename: PO_1
xyzclusternumber: 3
xyzmessagestoreid: 9
John Doe is a user of a hypothetical mail system called XYZ Mail.
Let's say mail arrives on an MTA called "mx.example.com", addressed
to "john@example.com". The MTA searches the directory for a mail
recipient with that address, and routes the message to "xyz-
gw.example.com", rewriting the SMTP envelope recipient address to
"John_Doe@xyz-gw.example.com", as per the 'mailRoutingAddress'. On
"xyz-gw.example.com", the message is gatewayed into the XYZ Mail
system and then dealt with as per other attributes.
Lachman [Page 7]
INTERNET-DRAFT LDAP Schema for Intranet Mail Routing May 1999
Here is an example of an LDAP entry representing a mailing list:
dn: cn=Scuba Group,o=Example Corp,c=US
objectclass: top
objectclass: groupOfUniqueNames
objectclass: inetLocalMailRecipient
objectclass: mailGroup
cn: Scuba Group
mail: scuba@example.com
mailhost: host42.example.com
mgrprfc822mailmember: joe@example.com
mgrprfc822mailmember: john@example.com
The Scuba Group is a mail group (mailing list) that includes two
members. A message addressed to "scuba@example.com" is routed to
"host42.example.com" where it is then resent to the mailing list
members. The 'mailGroup' object class is specified elsewhere [10].
Here is an example of an LDAP entry representing a forwarding alias:
dn: cn=Jane Roe Forwarding Alias,o=PU,c=US
objectclass: top
objectclass: inetLocalMailRecipient
objectclass: mailForwardingAlias
mail: janeroe@pu.edu
mailhost: mail.pu.edu
mailforwardingaddress: janeroe@elsewhereville.edu
cn: Jane Roe Forwarding Alias
This entry uses a hypothetical object class 'mailForwardingAlias'
that is not specified here, but is used as an example of how an LDAP
entry might represent such a recipient type. A message addressed to
"janeroe@pu.edu" is routed to "mail.pu.edu" where it is then
forwarded. In this case, Jane Roe may be a former student of a
university called PU, and they are forwarding her mail to her new
address elsewhere.
5. Security Considerations
As in all cases where account information is stored in an LDAP-based
directory service, network administrators must be careful to ensure
that their directory service controls users' access to the entries
and attributes stored therein, according to site policy. In
particular, mail routing information should not be accessible from
outside the organization, since it is intended for use only by MTAs
within the organization.
6. Acknowledgements
Lachman [Page 8]
INTERNET-DRAFT LDAP Schema for Intranet Mail Routing May 1999
The 'inetLocalMailRecipient' object class is based on an earlier
design done by the Netscape Messaging and Directory Server teams,
which was implemented and deployed to customers as part of Netscape
Messaging Server. Various team members contributed to the design,
including Bill Fitler, Bruce Steinback, Prabhat Keni, Mike Macgirvin,
John Myers, John Kristian, Tim Howes, Mark Smith, and Leif Hedstrom.
Thanks also to Jeff Hodges of Stanford for contributing to the early
design discussions, and to the other participants in the IETF LASER
BOF, including, from Sun Microsystems, John Beck, Anil Srivastava,
and Darryl Huff.
7. References
[1] W. Yeong, T. Howes, S. Kille, "Lightweight Directory Access
Protocol", RFC 1777, March 1995.
[2] J. Postel, "Simple Mail Transfer Protocol", STD 10, RFC 821,
August 1982.
[3] D. Crocker, "Standard for the Format of ARPA Internet Text
Messages", STD 11, RFC 822, August 1982.
[4] "Information Processing Systems - Open Systems Interconnection -
The Directory: Overview of Concepts, Models and Service", ISO/IEC JTC
1/SC21, International Standard 9594-1, 1988.
[5] C. Partridge, "Mail routing and the domain system", STD 14, RFC
974, January 1986.
[6] R. Braden, "Requirements for Internet hosts - application and
support", STD 3, RFC 1123, October 1989.
[7] M. Wahl, A. Coulbeck, T. Howes, S. Kille, "Lightweight X.500
Directory Access Protocol (v3): Attribute Syntax Definitions", RFC
2252, December 1997.
[8] P. Barker, S. Kille, "The COSINE and Internet X.500 Schema", RFC
1274, November 1991.
[9] T. Howes, "The String Representation of LDAP Search Filters",
RFC 2254, December 1997.
[10] B. Steinback, "Using LDAP for SMTP Mailing Lists and Aliases",
Internet-Draft (work in progress).
[11] G. Good, "The LDAP Data Interchange Format (LDIF) - Technical
Specification", Internet-Draft (work in progress).
Lachman [Page 9]
INTERNET-DRAFT LDAP Schema for Intranet Mail Routing May 1999
[12] M. Smith, "The inetOrgPerson Object Class", Internet-Draft
(work in progress).
8. Author's Address
Hans Lachman
Netscape Communications Corp.
501 East Middlefield Road
Mountain View, CA 94043
Phone: (650) 254-1900
EMail: lachman@netscape.com
Lachman [Page 10]
INTERNET-DRAFT LDAP Schema for Intranet Mail Routing May 1999
9. Full Copyright Statement
Copyright (C) The Internet Society (1999). All Rights Reserved.
This document and translations of it may be copied and furnished
to others, and derivative works that comment on or otherwise
explain it or assist in its implementation may be prepared, copied,
published and distributed, in whole or in part, without
restriction of any kind, provided that the above copyright notice
and this paragraph are included on all such copies and derivative
works. However, this document itself may not be modified in any
way, such as by removing the copyright notice or references to the
Internet Society or other Internet organizations, except as needed
for the purpose of developing Internet standards in which case the
procedures for copyrights defined in the Internet Standards
process must be followed, or as required to translate it into
languages other than English.
The limited permissions granted above are perpetual and will not
be revoked by the Internet Society or its successors or assigns.
This document and the information contained herein is provided on
an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET
ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Lachman Expires: November 1999 [Page 11]
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