INTERNET-DRAFT H. Lachman Intended Category: Informational Netscape Communications Corp. Filename: draft-lachman-laser-ldap-mail-routing-02.txt G. Shapiro Sendmail, Inc. Expires: July 2001 January 2001 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." 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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 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. Lachman, et. al. [Page 1] INTERNET-DRAFT LDAP Schema for Intranet Mail Routing January 2001 1. Conventions Used in this Document The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY" and "OPTIONAL" in this document are to be interpreted as described in [9]. 2. 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. 3. Overview Email systems deployed in large organizations must scale to support large numbers of users and email servers. This means using email addresses that are independent of particular mailbox server hosts; thus an "email routing server" that receives mail sent to the host-independent (or high-level or top-level or domain ...) address and routes it to the appropriate mailbox server. For scalability there should be many routing servers providing identical service. A set of such servers and the mailbox servers they route to form an "email domain". Lachman, et. al. [Page 2] INTERNET-DRAFT LDAP Schema for Intranet Mail Routing January 2001 This specification describes the basic function of the routing server, including data elements to support per-recipient routing info, and use of LDAP-based directory service to support multiple servers sharing the routing info data. The routing function is distinguished from other MTA-transfer operations. The 'inetLocalMailRecipient' object class and associated attributes identify an LDAP entry as representing an SMTP mail recipient (in the sense "recipient" is used in [2]). 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. Once on the target MTA, a message is handled according to local conventions (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. Any domain that uses LDAP-based routing MUST support LDAP-based routing at all MTAs responsible for the domain. All other MTAs that do not support LDAP-based routing MUST forward mail for that domain to MTAs that do, using MX records or other local conventions. The target MTA checks to see if the destination domain of the recipient address is one that it is responsible for and that uses LDAP-based routing. If so, the MTA checks for matching e-mail addresses in LDAP by looking up the envelope recipient address in LDAP using the object class described in section 4.1 and the attribute discussed in section 4.2. If an unambiguous match is returned, the MTA interprets the routing attributes as described in section 4.3. 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 'mailLocalAddress' and 'mailHost' attribute values in an 'inetLocalMailRecipient' entry must be DNS domain names that are local to the organization. (e.g., within the organization's Intranet or by deemed local by other local conventions outside the scope of this standard). An MTA should not look for or use 'inetLocalMailRecipient' entries or attributes if that MTA is not authoritative for the right-hand side of the recipient address in question. Lachman, et. al. [Page 3] INTERNET-DRAFT LDAP Schema for Intranet Mail Routing January 2001 LDAP entries that are not 'inetLocalMailRecipient' entries should be ignored by MTAs for the purpose of routing. 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. 4. Object Class and Attribute Definitions The 'inetLocalMailRecipient' object class and associated attributes are defined (using syntaxes given in [7]) as follows. 4.1 The inetLocalMailRecipient Object Class ( 2.16.840.1.113730.3.2.[[TBD]] NAME 'inetLocalMailRecipient' SUP top AUXILIARY MAY ( mailLocalAddress $ mailHost $ mailRoutingAddress ) ) 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. In any case of an entry containing the 'inetLocalMailRecipient' object class, attributes defined in this document MUST be interpreted as specified in this document. 4.2 Address Attribute ( 2.16.840.1.113730.3.1.13 NAME 'mailLocalAddress' DESC 'RFC 822 email address of this recipient' EQUALITY caseIgnoreIA5Match SYNTAX '1.3.6.1.4.1.1466.115.121.1.26{256}' ) The 'mailLocalAddress' attribute is used to specify email addresses, for the recipient; for example, "nickname@example.com". The address conforms to the syntax of an 'addr-spec' as defined in [3]. The 'mailLocalAddress' attribute MUST contain all local addresses that represent each recipient of the target MTA. Commonly, the value of the 'mail' attribute should also be among the addresses listed in the 'mailLocalAddress' attribute if it is expected to be used for LDAP mail routing. Lachman, et. al. [Page 4] INTERNET-DRAFT LDAP Schema for Intranet Mail Routing January 2001 When determining the disposition of a given message, MTAs using LDAP (directly or indirectly) to route mail MUST search for an entry with object class 'inetLocalMailRecipient' and a 'mailLocalAddress' attribute matching the message's recipient address. If exactly one matching entry is found, MTAs MUST regard the message as being addressed to the entity that is represented by the directory entry. If multiple entries are found, the results of the lookup MUST be treated as unsuccessful and should be handled by the MTA in some locally-appropriate way, such as returning a DSN [10] to the sender. If there is no match found by the above, MTAs SHOULD have the capability of searching for the recipient domain against the 'mailLocalAddress' attribute using the "wildcard domain" address "@<full-local-domain>" , e.g., "@example.org". In other words, if mail arrives for "someone@example.org", and there is no recipient with that address specified as 'mailLocalAddress', then the recipient with the wildcard domain address should receive the mail. MTAs MAY do other searches but only after the above are done. In short, the address attribute 'mailLocalAddress' may be used by an LDAP entry to answer the question "what is/are this account's email address(es)?" 4.3 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 handleable. 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. Normal mail routing requirements (i.e., use of MX records [5]) apply to the specified hostname unless overridden by local conventions. In other words, the mail should be sent to the specified host without changing the recipient address. The hostname is specified as a fully-qualified DNS hostname with no trailing dot (e.g., "host42.example.com"). If the 'inetLocalMailRecipient' object class is present, the 'mailHost' attribute for each entry MAY contain a value. If it does, that value MUST be the fully qualified name of the server containing the host MTA for this person. If 'mailHost' is present then it MUST be taken as the host for this user, and all mail to this user MUST be routed to this machine. Lachman, et. al. [Page 5] INTERNET-DRAFT LDAP Schema for Intranet Mail Routing January 2001 ( 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 MUST conform to the syntax of an 'addr-spec' in [3]. An intermediary MTA MUST use this information to route the message to the MTA that handles mail for this recipient, e.g., the envelope address MUST be rewritten to this value. 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. 'mailRoutingAddress' MAY be used as an alternative to 'mailHost', and is intended to have the same effect as 'mailHost' except that 'mailRoutingAddress' is 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, MTAs MUST interpret it to mean 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. Absence of both 'mailHost' and 'mailRoutingAddress' MAY be considered an error, unless "location-independent" recipient types 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. Lachman, et. al. [Page 6] INTERNET-DRAFT LDAP Schema for Intranet Mail Routing January 2001 The following possibilities exist as a result of an LDAP lookup on an address: mailHost is mailRoutingAddress is Results in ----------- --------------------- ---------- set to a set mail routed to "local" host mailRoutingAddress set to a not set delivered to "local" host original address set to a set relay to mailHost remote host using mailRoutingAddress set to a not set original address remote host relayed to mailHost not set set mail routed to mailRoutingAddress not set not set error or "location-independent" The term "local" host above means the host specified is one that the local (target) MTA considers to be a local delivery. The local MTA MAY rewrite the original address when mailRoutingAddress is not set if local conventions warrant the change. 5. Examples The following examples illustrate possible uses of the 'inetLocalMailRecipient' object class. Note that the examples include attributes defined outside of this document to demonstrate a complete record. The existence of these attributes in the example is not an indication that these attributes are used for LDAP-based mail routing (e.g., the 'mail' is not used for mail routing). 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 Lachman, et. al. [Page 7] INTERNET-DRAFT LDAP Schema for Intranet Mail Routing January 2001 mailLocalAddress: joe@example.com mailLocalAddress: joe@another.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". That MTA searches the directory for a mail recipient with that address, using an LDAP search filter [8] such as: (&(objectClass=inetLocalMailRecipient) (mailLocalAddress=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 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). 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 mailLocalAddress: john@example.com mailRoutingAddress: John_Doe@xyz-gw.example.com xyzPostOfficeName: PO_1 xyzClusterNumber: 3 xyzMessageStoreId: 9 Lachman, et. al. [Page 8] INTERNET-DRAFT LDAP Schema for Intranet Mail Routing January 2001 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". That 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. 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 mailLocalAddress: 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. Here is an example of an LDAP entry representing a forwarding alias: dn: cn=Jane Roe Forwarding Alias,o=Example,c=US objectClass: top objectClass: inetLocalMailRecipient objectClass: mailForwardingAlias mail: janeroe@example.org mailLocalAddress: janeroe@example.org mailHost: mail.example.org mailForwardingAddress: janeroe@elsewhere.example.com 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@example.org" is routed to "mail.example.org" where it is then forwarded. In this case, Jane Roe may be a former member of the Example Organization, and they are forwarding her mail to her new address elsewhere. Lachman, et. al. [Page 9] INTERNET-DRAFT LDAP Schema for Intranet Mail Routing January 2001 6. 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. 7. Acknowledgments 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. 8. References [1] M. Wahl, T. Howes, S. Kille, "Lightweight Directory Access Protocol (v3)", RFC 2251, December 1997. [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] T. Howes, "The String Representation of LDAP Search Filters", RFC 2254, December 1997. Lachman, et. al. [Page 10] INTERNET-DRAFT LDAP Schema for Intranet Mail Routing January 2001 [9] S. Bradner, "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [10] K. Moore, "SMTP Service Extension for Delivery Status Notifications", RCP 1891, January 1996. 9. Authors' Addresses Hans Lachman Netscape Communications Corp. 501 East Middlefield Road Mountain View, CA 94043 Phone: (650) 254-1900 EMail: lachman@netscape.com Gregory Neil Shapiro Sendmail, Inc. 6603 Shellmound Street Emeryville, CA 94608-1042 Phone: +1 510-594-5522 Fax: +1 510-594-5411 EMail: gshapiro@sendmail.org X. Change Summary X.1.1 Substantive changes between draft-lachman-laser-ldap-mail-routing-00.txt and draft-lachman-laser-ldap-mail-routing-01.txt (i) Added Gregory Neil Shapiro as another author. (ii) Changed Draft heaer. (iii) Added "Conventions Used in this Document" section. (iv) Replaced RFC mentions with reference numbers. (v) Add new MUST/SHOULD/MAY sections to bring more in line with RFC documents. (vi) Clarify job of MTA in Overview by adding third paragraph. (vii) mailRoutingAddress can be outside of administrative control. (viii) Eliminated use of 'mail' attribute for mail routing. (ix) Changed name of 'mailAlternateAddress' to 'mailLocalAddress'. (x) Remove "routable" from 'mailLocalAddress' description. (xi) Clarify which addresses MUST be in 'mailLocalAddress'. (xii) Allow for multiple responses if they all have the same routing attribute values. (xiii) Clarify use of MX records on routing attributes. (xiv) Add a table to clarify use of 'mailHost' and 'mailRoutingAddress'. (xv) Remove document weakening statements from section 5. (xvi) Only use reserved domains (example.com, example.org) in examples. (xvii) Clean up references (xviii) Added section X to list the changes between draft versions. Lachman, et. al. [Page 11] INTERNET-DRAFT LDAP Schema for Intranet Mail Routing January 2001 X.1.2 Substantive changes between draft-lachman-laser-ldap-mail-routing-01.txt and draft-lachman-laser-ldap-mail-routing-02.txt (i) Changed Intended Category from Standard Track to Informational. (ii) Removed references to mailGroup document which has expired. (iii) Add additional Overview text from RL 'Bob' Morgan. (iv) If a domain uses LDAP-based routing, require all MTAs in that domain to either use LDAP for routing or forward mail to an MTA which uses LDAP for routing. (v) Add more text regarding "local" domain. (vi) Tighten rules for better interoperability. Multiple, matching results is now treated as an unsuccessful lookup. (vii) Tighten rules for better interoperability. Change the action for a lookup which returns both a 'mailHost' and 'mailRoutingAddress' to a MUST (from a MAY). (viii) Point out that examples contain attributes which are not part of this spec and should not be used for mail routing (specifically, 'mail'). (ix) Clean up text. (x) NOTE: Still need vendor-neutral OIDs for the objectClass and attributes. 10. Full Copyright Statement Copyright (C) The Internet Society (1999-2001). 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, et. al. [Page 12]