Recipe7.17.Sharing an SMTP Domain Between Exchange and a Foreign Mail System

Recipe 7.17. Sharing an SMTP Domain Between Exchange and a Foreign Mail System

Problem

You have another mail system within your organization that must share the same SMTP domain namespace with Exchange and you need them to coexist.

Solution

Using a graphical user interface

If you need to use the foreign mail system as the final authoritative system:

1. Open the Exchange System Manager (Exchange System Manager.msc).

2. Expand the organization Recipients Recipient Policies.

3. Right-click the default policy and select Properties.

4. Click the E-mail Addresses tab.

5. Click New, select SMTP Address, and click OK.

6. Fill in the Address field with the value @local and click OK.

7. Check the checkbox beside the new SMTP domain and click Set as Primary.

8. Click Apply. When you are asked if you wish to apply the change to all recipients, click Yes. You may be asked this multiple times.

9. Open the property sheet of the recipient policy that contains the domain you wish to share.

10. Click the E-mail Addresses tab.

11. Click Edit and clear the This Exchange organization is responsible for all mail delivery to this address checkbox. Click OK twice.

12. Create a new recipient policy and name it User Addresses.

13. Click the Filter tab, click Modify, and adjust the filter to apply to all users. Click OK on the Find Exchange Recipients screen.

14. Click the E-mail Addresses tab and set the shared domain as the primary address. Click OK.

15. Create a new SMTP connector (see Recipe 7.4) with an address space of the shared domain. This connector should have the Forward all mail through this connector to the following smart hosts checkbox enabled.

16. Configure the smart host using either the FQDN or the [IPAddress]syntax.

17. Check the Allow messages to be relayed to these domains checkbox and click OK.

If you need to use Exchange as the final authoritative system:

1. Create Active Directory contact objects for each recipient on the other mail system. Their email addresses should be in the form [e-mail], where the string host.domain is not defined as a valid SMTP address namespace in the Exchange organization's recipient policies.

2. Create a new SMTP connector (see Recipe 7.4) with an address space of host.domain. This connector should be configured to deliver all messages directly to the appropriate host, using the [host.domain] syntax to avoid MX lookups in DNS.

3. Configure the other mail system to forward any unresolved messages to Exchange.

4. Configure your DNS and firewall so that incoming SMTP traffic is handled by the other mail system.

Discussion

Conceptually, sharing a domain between Exchange and another mail system is easy:

• Decide which system will be the final authoritative server for the domain. You must have a final authoritative server; this server will generate the NDRs for any nonmatched recipients.

• Configure incoming SMTP mail to go to the nonauthoritative system first.

• Configure the nonauthoritative system to pass all unresolved mail for the domain to the authoritative system.

The devil is in the details, as always. MS KB 315591 provides two methods for configuring Exchange as the nonauthoritative system; we have summarized the first method, which provides domain-by-domain control, in our recipe. The second method shares all domains for which the Exchange server is configured to handle mail and is not covered in this recipe.

There is a per-domain setting for each domain specified in a recipient policy that determines whether Exchange is authoritative for the domain. By default, this setting is enabled. The first hurdle to jump is that Exchange must be authoritative for the primary address in the default recipient policy.

Steps 2-8 of the recipe create a new primary address (@local) on the default recipient policy, for which Exchange is authoritative.

Steps 9-11 configure Exchange as nonauthoritative on the shared domain.

Steps 12-14 are optional and permit your users to retain their primary email addresses in the shared domain.

Steps 15-17 permit Exchange to relay unresolved messages to the authoritative mail system.

See Also

"Supporting Two SMTP Mail Domains and Sharing an SMTP Mail Domain with Another System" in Chapter 6, "Deployment Scenarios for Internet Connectivity," of the Exchange Server 2003 Transport and Routing Guide on the TechNet web site, MS KB 315591 (XCON: Authoritative and non-authoritative domains in Exchange 2000), MS KB 319759 (XADM: How to configure Exchange 2000 Server to forward messages to a foreign messaging system that shares the same SMTP domain name space), and MS KB 321721 (XCON: Sharing SMTP Address Spaces in Exchange 2000 Server and Exchange Server 2003)