The Accepted Domain in Microsoft Exchange Server is a SMTP namespace for which the exchange mail server is responsible to give all mail service right. Accepted domain in exchange server is a set of characters called string for which exchange organization is Authoritative and the accepted domain is created first when the Hub Transport Server role is installed. When the exchange server authorities a domain then it is responsible to handle mail recipient mail delivery inside the exchange environment and outside the exchange environment.
Microsoft Exchange Server is enabled with powerful concept that only accepted domain can be considered as active part of internal or external email flow, basically accepted domain is any SMTP namespace which have all mail server right and accepted as mail server authoritative. In exchange 2007 a new terminology is introduced to describe email flow and which email will be sent to whom is called Accepted Domain.
The Microsoft described accepted domain as "An accepted domain is any Simple Mail Transfer Protocol (SMTP) name space for which the Microsoft exchange organization sends or receive inbound or outbound emails" basically the accepted domain relies in one of the these three category Authoritative, Internal Relay and External Relay any SMTP accepted domain belongs to these three types mail server field. When you create an accepted domain in exchange server then you need to choose one from listed below.
Before starting discussion on these domain types lets first discuss how to configure accepted domain in exchange server. A domain can be configured as accepted domain in exchange environment using organization setting of Exchange Management Console (EMC) but this process requires Exchange Administrators right to configure it. The accepted domains will be created for the complete exchange environment on Hub Transport Server or Edge Transport Server.
When the first Hub Transport Server is installed then the exchange server creates a new accepted domain and that domain is called the authoritative domain and it will be created with the internal active directory name not with the registered SMTP domain name. For Example if the internal active directory domain name is abc.mailtest and the registered SMTP domain name is abc.com then the authoritative domain name will be created as the abc.mailtest and you will have to create an additional accepted authoritative domain for the registered SMTP domain which is abc.com.
Note: - If you have exchange server with installed Edge Server role then no accepted domain will be created automatically in this situation you need to create authoritative domain manually or you need to synchronize these accepted domain with Edge Sync from your internal exchange organization. Now before discussing internal relay domain lets first understand what relay domain is then move to main segment.
Relay Domain: - The concept of relay domain is comes when we found that there is no authoritative domain for specific domain but the DNS MX (Mail Exchange) record points to the exchange hub transport or edge transport server, the sending email server relays all emails to exchange server. If the SMTP Domain is not a part of authoritative domain then the sending server tries to establish connection and relay through the exchange server and exchange server accepts this message and relays it to an internal relay domain or external relay domain.
Configuring an Internal Relay Domain means forwarding all emails which does not have corresponding mailbox in the exchange organization but the email address are in the contact list of exchange. The contacts have an email address which belongs to other messaging system then the email from the internet is relayed for this domain through hub transport server in the exchange organization.
For Example let us consider that an organization has two forests with exchange server installed and you want stablish a connection between then so that they can communicate to each other to achieve this you need to use a system that synchronizes the email addresses between these two forests. For this you can use IIPF (Identity Integration Feature Pack) or its advance mechanism MIIS (Microsoft Identity Integration Server). Now the email message from the internet which is addressed to recipient to internal relay domain are received and processed by Edge Transport Server and then transferred to Hub Transport server in same organization and the hub transport server which is responsible to routing the message and it will route the message to Hub Transport Server of the other Exchange Organization.
The External Relay Domain is different from the Internal Relay Domain because when you configure an external relay domain messages are relayed to an email server which is outside your exchange environment. In External relay the messaged are transferred through Exchange Edge Transport Server. The External relay domain MX (Mail Exchanger) is configured to route the emails to exchange organization and the exchange mail server accepts the email messages from this domain name and will route message to other domain through a SMTP Send Connector that you have configured in Exchange installation process and this send connector relays the message to the External Relay Domain.
You can create new accepted domain using PowerShell Commands but be careful while running the commands because a slight mistake will show the error here I am giving you the commands which you can use.
Create a New Accepted Authoritative Domain
New-AcceptedDomain -Name "mailtest" -DomainName mailtest.org - DomainType Authoritative
Creating a new internal relay domain
New-AcceptedDomain -Name "IT Training" -DomainName it-training.de - DomainType InternalRelay
Creating a new external relay domain
New-AcceptedDomain -Name "language" -DomainName language.org - DomainType ExternalRelay
Conclusion
In this article I have tried to discuss accepted domain in exchange server and its all related components like authority domain, internal relay domain and external relay domain in simple words and I hope that this effort will be helpful for you.