After you configure the mail system that is used by Fourth Coffee Company to route outgoing Internet mail using SMTP through your Exchange server, you then need to enable Address Rewrite on the SMTP virtual servers in your Exchange organization that are responsible for accepting mail from the subsidiary company's mail system. In this example, you enable address rewrite on all SMTP virtual servers that accept mail from the subsidiary company, Fourth Coffee.

The following conditions must exist for Address Rewrite to work properly:

• The message is externally submitted SMTP mail that is sent to the Exchange bridgehead server.
  
• E-mail messages are destined to the Internet.
  

Internal mail or mail sent from other Exchange servers in your organization to the bridgehead server where address rewrite is enabled bypass address rewrite. There is one exception; mail submitted using Outlook Express or any other SMTP client undergoes an address rewrite on this bridgehead server.

Remember that the intent of this tool is to rewrite addresses only for mail coming from the subsidiary company (externally SMTP submitted) into your company's e-mail servers and then destined to the Internet.

You can download the Address Rewrite tool (exarcfg) from the Microsoft website at http://go.microsoft.com/fwlink/?LinkId=25097. After you download the tool, use the following procedure to enable address rewrite on the appropriate SMTP virtual servers.

For detailed instructions, see How to Enable Address Rewrite by Using the Exarcfg Tool.

In Active Directory Users and Computers, you must create a contact for each user on the Fourth Coffee company mail system. Each contact must have a target address of fourthcoffee.com and a primary SMTP address of contoso.com.

The target address appears on the Exchange General tab of a contact's properties. You set the primary SMTP address on the E-mail Address tab of a contact's properties. You can use an automated process to add these contacts to Active Directory, or you can perform the steps manually.

The How to Create a Contact in Active Directory procedure shows how to create a contact in Active Directory manually by using the target address of the non-Microsoft mail system, which is Fourth Coffee in this example, and a primary SMTP address that is used by your Exchange organization, which is Contoso in this example.

To accept mail for Fourth Coffee Company users, an administrator at Contoso creates an SMTP connector to fourthcoffee.com and specifies each SMTP virtual server that accepts incoming Internet mail as a local bridgehead server for the connector. This connector is configured with an address space of the SMTP domain that is used by Fourth Coffee (fourthcoffee.com) and is configured to relay messages to this domain. To do this, the administrator opens the SMTP connector's properties, clicks the Address space tab, and then selects the Allow messages to be relayed to this domain check box.

The following figure illustrates the topology that is used by Contoso and Fourth Coffee. Note that one Exchange server accepts outgoing mail from Fourth Coffee, and a separate server routes incoming mail to Fourth Coffee users. The SMTP virtual server that accepts mail from Fourth Coffee can also function as an outbound gateway server, but this is not a requirement. This SMTP virtual server can either route Internet mail that is received from Fourth Coffee users directly to the Internet, or it can route this mail to the appropriate gateway server

Before you configure your recipient policy for the SMTP mail domain that you want to share, you must determine if Exchange is authoritative over the domain.

Remember, depending on whether Exchange 2003 is authoritative or nonauthoritative, Exchange handles e-mail messages differently for particular SMTP addresses. Because Exchange does not forward messages that it cannot resolve locally for an authoritative domain, you must ensure that Exchange is not authoritative over the SMTP mail domain you want to share.

For detailed instructions, see How to View the Setting that Determines Whether Exchange Server is Authoritative.

When configuring the recipient policy for the SMTP mail domain that you want to share, there are three possible scenarios you may encounter:

• Scenario 1   The SMTP mail domain that you want to share exists on the default recipient policy.
  
• Scenario 2   The SMTP mail domain that you want to share exists on another recipient policy.
  
• Scenario 3   The SMTP mail domain that you want to share does not exist on a recipient policy.
  

Scenario 1: Configuring a Shared SMTP Domain that Exists on the Default Recipient Policy

You cannot set Exchange to be nonauthoritative over the default recipient policy's primary SMTP address space. To prevent Exchange from being authoritative over this domain, you need to change the default recipient policy by adding a new primary address space that is strictly for internal use. This address could be similar to @localhost, signifying that it is used solely for internal mail flow within your Exchange organization. After you add the new address space, you must make the shared address space nonauthoritative.

To configure Exchange to share a mail domain that exists as the primary address space on the default recipient policy, you must perform the following tasks:

1. On the default recipient policy, add a new primary address space over which Exchange is authoritative, and then make the shared address space nonauthoritative.
   
2. Create a second recipient policy that has the same search filter as the default recipient policy. Then, assign the second recipient policy a higher priority than the default recipient policy so the reply-to or return address is displayed as the shared address space.
   This step is necessary because Exchange uses the primary address space as the reply-to address that is displayed in outgoing mail. Because you want outgoing messages to display the shared namespace on the reply-to line, you must create another recipient policy that is also nonauthoritative but has a higher priority; therefore, Exchange uses this address space on the return address of outgoing mail. Because the new recipient policy is not the default recipient policy, you can make this address space nonauthoritative.
   

Perform the How to Modify the Default Recipient Policy procedure to create a new primary address space on the default recipient policy and make the shared address space nonauthoritative.

Changing the default recipient policy in this way causes Exchange to use the new primary address as the return or reply-to address in outgoing e-mail messages. In the example above, all users in this policy now have a return e-mail address that matches the new primary address space of @localhost. Because you want all your users to have the return address of the shared mail domain (in this case, contoso.com), you must create a new recipient policy with a higher priority recipient policy that contains the contoso.com address space. Exchange uses the higher priority recipient policy on the return address. Furthermore, because this recipient policy is not the default recipient policy, you can make it nonauthoritative. (Remember, this address space must be nonauthoritative for Exchange to route it through the connector to the external system.)

Perform the How to Create a Higher Priority Recipient with the Shared Mail Domain procedure to create a higher priority recipient policy so that outgoing e-mail messages display the correct return (reply-to) address.

Scenario 2:  The SMTP Domain You Want to Share Exists on Another Recipient Policy

If the SMTP domain that you want to share is not on the default recipient policy, you can make the address space nonauthoritative.

For detailed instructions, see How to Modify an Existing Recipient Policy for the SMTP Domain that You Want to Share.

Scenario 3: The SMTP Domain You Want to Share Does Not Exist on a Recipient Policy

If the SMTP domain that you want to share does not exist on a recipient policy, you can create a new recipient policy with the address space and make it nonauthoritative.

For detailed instructions, see How to Create a New Recipient Policy for an SMTP Mail Domain that Does Not Exist on a Recipient Policy.

Now that Exchange 2003 is nonauthoritative for the shared SMTP domain, when Exchange 2003 cannot find a matching address in Active Directory, it attempts to locate an external path to this domain. To find this path, Exchange first searches for a connector and then checks Domain Name System (DNS). Unless the mail exchanger (MX) record for that domain already points to the server on which the other mail system resides (in many cases the MX record points to the Exchange 2003 server itself), you must create an SMTP connector to route the mail to a specific host.

For detailed instructions, see How to Create an SMTP Connector to Route Mail to a Specific Host.

After you configure these settings, when Exchange 2003 cannot locate a local address match in that SMTP domain, Exchange forwards the mail to the host that has the matching address space, as specified on the SMTP connector.