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# SMTP: GW0645: Configuring the SMTP Gateway & DNS

Article ID: 101459

Article Last Modified on 10/30/2006

APPLIES TO

- Microsoft Mail Gateway to SMTP 3.0

This article was previously published under Q101459

## SUMMARY

The application note titled "Configuring the SMTP Gateway and Domain Name Service (DNS)," GW0645, concentrates on how to properly configure the Domain Name Service (DNS) to route Microsoft Mail messages.
You can obtain this Application Note from the following sources:

- Microsoft Product Support Services

For complete information, see the "To Obtain This Application Note" section at the end of this article.

## MORE INFORMATION

Here is the text of the application note:

    ======================================================================
      Microsoft(R) Product Support Services Application Note (Text File)
       Configuring the SMTP Gateway and Domain Name Service (DNS): MAIL
                              GATEWAY TO SMTP 3.0
    ======================================================================
                                                       Revision Date: 7/93
                                                          No Disk included

    The following information applies to Microsoft Mail version 3.0.

     --------------------------------------------------------------------
    | INFORMATION PROVIDED IN THIS DOCUMENT AND ANY SOFTWARE THAT MAY    |
    | ACCOMPANY THIS DOCUMENT (collectively referred to as an            |
    | Application Note) IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY      |
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    | PARTICULAR PURPOSE. The user assumes the entire risk as to the     |
    | accuracy and the use of this Application Note. This Application    |
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    | conditions: 1) All text must be copied without modification and    |
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    | on the disk(s) must be copied without modification [the MS-DOS(R)  |
    | utility DISKCOPY is appropriate for this purpose]; 3) All          |
    | components of this Application Note must be distributed together;  |
    | and 4) This Application Note may not be distributed for profit.    |
    |                                                                    |
    | Copyright 1993 Microsoft Corporation. All Rights Reserved.         |
    | Microsoft and MS-DOS are registered trademarks and Windows         |
    | is a trademark of Microsoft Corporation.                           |
     --------------------------------------------------------------------

    INTRODUCTION
    ============

    The Microsoft Mail Gateway to SMTP software depends on another host on
    the TCP/IP side of the gateway to route messages from the Microsoft
    Mail world to the TCP/IP world. This routing host is referred to in
    the "Microsoft Mail Gateway to SMTP" manual as the "smarthost". The
    smarthost routes mail both to and from the Microsoft Mail world by
    using a group of routing files collectively referred to as the Domain
    Name Service. The term Domain Name Service (DNS) is a generic term
    common to all implementations of TCP/IP, not just Microsoft's gateway,
    and is defined in RFC 1034 and RFC 1035. Thus, you need to configure
    two hosts when setting up an SMTP gateway: the host with Microsoft
    Mail SMTP gateway software (commonly referred to as the gateway PC)
    and the smarthost designated as the DNS. This article concentrates on
    how to properly configure the DNS to route Microsoft Mail messages.

    CONFIGURING THE DNS
    ===================

    The DNS files include several different routing records. The two types
    of records needed to route Microsoft Mail records are the address
    record and the mail exchanger record.

    Address Record
    --------------

    The mail address record, also known as an A record in the zone file of
    the DNS, defines the IP address to a domain name. For example,
    123.123.123.123 might be defined as hostname.dept.company.com.

    Mail Exchanger Record
    ---------------------

    The mail exchanger record, also known as an MX record in the zone file
    of the DNS, associates a domain name to a domain name defined in an
    address record. For example, postoffice.network.company.com might be
    associated with hostname.dept.company.com. The exact syntax for
    defining mail exchanger records depends on the TCP/IP software the
    smarthost is running.

    CONFIGURING THE SMTP GATEWAY TO MATCH THE DNS
    =============================================

    Parts of the SMTP gateway configuration should match exactly what is
    defined as an A record and MX record(s) in the DNS. Specifically, when
    you select the Administrator program Gateway, SMTP, Setup command, the
    Internet Name Of Gateway field must match exactly the domain name
    defined in the A record. This is the domain name of the dedicated PC
    running the Microsoft Mail SMTP gateway.

    NOTE: The smarthost does not have to be the host that has the DNS
    running on it. This depends on your site's implementation of the
    TCP/IP network and which machine will be responsible for receiving
    mail from the gateway.

    Also, when you select the Administrator program Gateway, SMTP, Address
    Map command, the SMTP Domain field must match exactly the domain name
    defined in an MX record in the DNS. The address map must contain all
    the Microsoft Mail (gateway and downstream) postoffices that will send
    and receive SMTP mail. Each SMTP Domain entry in the address map must
    have a corresponding MX record that associates it to the gateway PC's
    domain name (Internet Name of Gateway).

    EXAMPLE
    =======

    To make the process clearer, let's follow a message from the SMTP
    world to the Microsoft Mail world, using the following assumptions:

     - The domain name of the gateway PC is msmailgwy.company.com, and its
       IP address is 123.123.123.123.

     - The two Microsoft Mail postoffices are named Sales and HQ, and the
       network name is Company. The gateway is attached to the Sales
       postoffice.

     - There is a user named Sparky on postoffice HQ. The DNS resides on a
       host with the IP address of 123.123.1.1.

    Configuring the Gateway
    -----------------------

    1. Set up the DNS with one A record defining msmailgwy.company.com to
       123.123.123.123.

    2. Set up an MX record for each postoffice. Set up one MX record to
       define all mail destined for HQ.company.com to be routed to host
       msmailgwy.company.com, and set up another MX record to define all
       mail destined for Sales.company.com to be routed to host
       msmailgwy.company.com.

       NOTE: The MX record for each postoffice including the SMTP HUB should
       map to the UNIX smart host NOT the SMTP gateway. If it maps to the
       SMTP gateway this will allow a foreign SMTP gateway on the Internet to
       connect to and hang the SMTP gateway. If the MX record maps to the
       UNIX smart host the SMTP gateway will only ever talk to the smart
       host.

    3. Select the Gateway, SMTP, Setup command to configure the following
       options:

          Domain Suffix:              .company.com
          Internet Name of Gateway:   msmailgwy.company.com
          IP Address of SMTP Router:  123.123.1.1

    4. Select the Gateway, SMTP, Postoffices command to configure the
       following options:

          company/HQ
          company/sales

    5. Select the Gateway, SMTP, Address Map command to configure the
       following options:

          Enter network name:         company
          Enter postoffice name:      HQ
          SMTP Domain:                HQ.company.com

       -and-

          Enter network name:         company
          Enter postoffice name:      Sales
          SMTP Domain:                Sales.company.com

    Sending Mail
    ------------

    1. Mail is sent from the SMTP world to a Microsoft Mail user. The
       sender types in the TO: field something similar to the following:

          Sparky@HQ.company.com

    2. The message arrives at the DNS for routing. The DNS looks in its
       files for HQ.company.com. It finds HQ.company.com as an MX record
       and routes the message to host msmailgwy.company.com. The DNS then
       looks in its files for msmailgwy.company.com. It finds
       msmailgwy.company.com as an A record and routes the message to the
       IP address 123.123.123.123.

    3. The gateway PC receives the message. It compares HQ.company.com to
       the entries in the address map until it finds a match. It finds a
       match, which tells the gateway PC that HQ.company.com is Company/HQ
       in the Microsoft Mail world.

    4. The gateway PC then delivers the message to the HQ postoffice.

       NOTE: The DNS is defined in the gateway PC's TCP/IP software
       configuration and in the Microsoft Mail SMTP gateway software (in
       the Administrator program Gateway, Setup, IP Address Of SMTP Router
       field).

### TO OBTAIN THIS APPLICATION NOTE

- If you are unable to access the source(s) listed above, you can have this Application Note mailed or faxed to you by contacting Microsoft Product Support Services.

## REFERENCES

Microsoft Mail Gateway to SMTP "Administrator's Guide," RFC 1034, RFC 1035.

Additional query words: wga appnotes

Keywords: KB101459