More businesses register multiple domain
names than ever before because it’s cheap and easy to do. Some
users have several e-mail addresses, all with different domain
names but delivered via the same mail server. If you aren’t hosting
more than one domain on your Exchange server, you probably will in
the near future.

Follow these steps to configure the Internet
Mail Service (IMS) to support multiple domains in Exchange 5.5:

  1. From the Exchange Server Administrator
    program, navigate to the Connections container, and double-click
    the Internet Mail Service object.
  2. From the Internet Mail Service
    Properties dialog box, select the Routing tab, and click
    Add.
  3. Enter the domain you want to add in the
    E-mail Sent To This Domain field, select the Should Be Accepted As
    “Inbound” option, and click OK.
  4. Repeat Steps 2 and 3 for each domain you need
    to support. When you’re finished adding domains, click OK to close
    the Internet Mail Service Properties dialog
    box.
  5. Stop and restart the Microsoft Exchange
    Internet Mail Service to make your changes take effect.

In order for mail from the new domains to be
delivered to your Exchange server, you’ll need to do some DNS work.
The DNS server that’s authoritative for each domain you host must
point the domain’s MX record to the same host A record that
contains the IP address of your SMTP host. If you don’t host your
own DNS, contact your ISP about making these changes.