Authoritative, Accepted, Relay domains
http://technet.microsoft.com/en-us/library/bb124423.aspx An accepted domain is any SMTP namespace for which a Microsoft Exchange organization sends or receives e-mail. Accepted domains include those domains for which the Exchange organization is authoritative. An Exchange organization is authoritative when it handles mail delivery for recipients in the accepted domain. Accepted domains also include domains for which the Exchange organization … Read more