Try to create an Active Directory design that is as simple as possible. Expand the directory tree with multiple subdomains and forests at a later date if needed.
Even if the organization has high bandwidth between sites, create a site to better control replication and traffic between sites.
When possible, DNS in an organization should be Microsoft DNS; however, Windows 2003 (and Windows 2000) also can be integrated with non-Microsoft DNS.
Minimize the number of servers needed by consolidating services into as few systems as possible.
Use the /3GB /USERVA=3030 switch in bootl.ini to optimize system memory in an Exchange Server with more than 1GB of RAM.
If the organization does not have a third-party antispam software program, enable the Microsoft Exchange 2003 antispam functionality to minimize unwanted mail.
