5.5 DNS and Exchange

If you're running Microsoft Exchange Server, you need to know how it interoperates with DNS, whether or not you're using the Microsoft DNS Server. Here are some subtle differences between the various versions of Exchange that run on Windows NT, Windows 2000, and Windows Server 2003:

• If you're using Exchange 4.x or 5.x on Windows NT, you can run Exchange without DNS. However, before you can install the Internet Mail Service (IMS, which is what Microsoft calls its SMTP server), you must have A and MX records defined for the host and domain on which you're installing the IMS. You also need to make sure that the Exchange server's DNS settings are set correctly so it can look up mail forwarders for outgoing mail.

• If you're using the SMTP server that comes with the Windows NT Option Pack, Internet Information Server 4.x, Windows 2000, or Windows Server 2003, you need an MX record if you want to receive mail; to send mail you only need access to a name server.

• If you're using Active Directory, you'll find that your need for DNS is pervasive: Active Directory depends on DNS to find domain controllers, global catalog servers, and other services. We'll cover the DNS needs of Active Directory in Chapter 8.

• Exchange 2000 uses Active Directory as its directory service, so it is totally dependent on the underlying OS's DNS setup. In particular, Exchange 2000 needs access to SRV records so it can find global catalog servers, instant messaging hosts, and domain controllers. Don't worry—SRV records are also covered in Chapter 8.