SMTP: GW0645: Configuring the SMTP Gateway & DNS

The information in this article applies to:

• Microsoft Mail Gateway to SMTP, version 3.0

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 Download Service (MSDL)
• Microsoft Product Support Services

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

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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

• Application Notes are available by modem from the Microsoft Download Service (MSDL), which you can reach by calling (206) 936-6735. This service is available 24 hours a day, 7 days a week. The highest download speed available is 14,400 bits per second (bps). For more information about using the MSDL, call (800) 936-4400 and follow the prompts. To obtain GW0645, download GW0645.EXE. GW0645.EXE is a compressed, self-extracting file. After you download GW0645, run it to extract the file(s) it contains.
• 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.