The following is a list of common configuration mistakes made by Small Business Server administrators that actually degrade the performance of the Small Business Server network:

• Configuring the ISA Server LAT to include the external IP address of the Small Business Server computer. The LAT is the table that ISA Server uses to determine how to route network traffic. If the external IP address of the Small Business Server computer is included in the LAT, then ISA Server will not know when to forward Internet traffic to the Internet. The LAT should contain only the local IP range of the Small Business Server network.
• Modifying the default configuration of the SMTP virtual server. Small Business Server Internet Connection Wizard will configure the SMTP virtual server with the correct permissions to allow secure and efficient e-mail exchange between the Small Business Server computer and the Internet. It is recommended that you not change these default settings.
• Changing the address space of the Small Business SMTP connector. Small Business Server Internet Connection Wizard creates an SMTP connector to deliver and receive e-mail to the Internet. The address space is set to *, with a cost of 1, which refers to all Internet addresses. Modifying this value from the default will result in some e-mails addressed to Internet domains not being delivered.
• Enabling ISA Firewall automatic discovery in Firewall Client. Automatic discovery is a feature of ISA Server that allows automatic configuration of Firewall Client on client computers. Since automatic discovery uses port 80, it will conflict with IIS which is running on port 80 of the internal network adapter. Instead, it is recommended that administrators configure the Firewall Client manually.
  Note: When Firewall Client is installed and configured using the Set Up Computer Wizard, this configuration is performed automatically.
• Installing Firewall Client on the Small Business Server computer. Due to the architecture of ISA Server, it is not possible to run Firewall Client on the same server as ISA Server. Attempting to do so will result in unpredictable network behaviour. To allow network services on the server to access the Internet, it is necessary to create an outbound packet filter in ISA Server.
• Configuring client computers to use the ISP's DNS server. All client computers in the Small Business Server network should be configured to use the Small Business Server DNS server for name resolution. The Small Business Server DNS service will forward Internet name requests to the ISP as necessary. If DHCP is being used on the Small Business Server computer, and client computers are configured to use dynamic IP addressing, the correct configuration is done automatically.