This post discuss how to configure Non-Authoritative Accepted Domains in SBS 2008. If you are not familiar with the concept of Accepted Domains in Exchange 2007, please refer to the following link before moving forward: http://technet.microsoft.com/en-us/library/bb124423(EXCHG.80).aspx
Three types of Accepted Domains exist in Exchange 2007. By default, SBS 2008 configures two Authoritative Accepted Domains for you; one for your .local namespace and one for your external FQDN. Authoritative domains are synonymous with enabling “This Exchange Organization is responsible for all mail delivery to this address” in Exchange 2003 recipient policies.
The other two types are Internal Relay and External Relay domains, which are Non-Authoritative domains. They must be created manually through the native Exchange interfaces if needed:[…]