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What are Accepted Domains

                An accepted domain is any SMTP domain name for which the 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. BTW, accepted domains also include domains for which the Exchange organization receives mail and then relays to an e-mail server that is outside the Active Directory forest for delivery to the recipient.

You must configure an accepted domain before that SMTP namespace can be used in an e-mail address policy. The accepted domain is automatically populated to the e-mail address policy editor. Each domain or sub-domain that you want to use as part of an e-mail address policy must have an explicit accepted domain entry.

Types of Accepted Domains

There are three types of accepted domains: authoritative, internal relay, and external relay.

Authoritative Domains

                 As noted in the example above, an organization might have more than one SMTP domain. These are the authoritative domains. In Exchange 2007, an accepted domain is considered authoritative when the Exchange organization hosts mailboxes for recipients in this SMTP domain. Meaning, Exchange 2007 will treat any incoming mail destined for a recipient on an authoritative domain as internal, and will "expect" to find a recipient with that SMTP address. If no such recipient exists, Exchange will return an NDR. By default, when the first Hub Transport server role is installed, one accepted domain is configured as authoritative for the Exchange organization. The default accepted domain is the fully qualified domain name (FQDN) for your forest root domain. The Edge Transport servers should always accept e-mail that is addressed to any of the organization's authoritative domains, and by default, no accepted domains are configured on the Edge Transport server role.

When dealing with e-mail destined for external SMTP domain names, we must configure the Exchange servers to "know" that they should accept incoming e-mail for these external domains, and perform a relay action on them. Needless to say, if we allow relaying of ALL external SMTP domains, spammers will soon find this out and begin using our servers as open relays, spamming the world through our servers. We can prevent this open relay by rejecting all e-mail that is not addressed to a recipient in the organization's authoritative domains. However, there are scenarios where an organization wants to let partners or subsidiaries relay e-mail through the Exchange servers. You can allow this by configuring accepted domains as relay domains. The Exchange organization receives the e-mail and then relays the messages to another e-mail server.

There are 2 options for configuring external domains: Either as an internal relay domain or as an external relay domain.

Internal Relay Domain

               When configuring an internal relay domain, the recipients in this domain do not have mailboxes in this Exchange organization but do have contacts in the global address list (GAL). Mail from the Internet is relayed for this domain through Hub Transport servers in this Exchange organization. In this scenario, the MX resource record for the external relay domain references a public IP address the Exchange 2007 organization that is relaying messages. The Edge Transport server receives the messages for recipients in the external relay domain and then looks for contacts in the GAL for those recipients. If it finds such a recipient, it will route the message to the e-mail system for the internal relay domain. The connector configuration of your organization determines how messages are routed.

External Relay Domain

                 When you configure an external relay domain, messages are relayed to an e-mail server that is outside the Exchange organization and outside the organization's network perimeter. The messages are relayed by the Edge Transport server. In this scenario, the MX resource record for the external relay domain references a public IP address the Exchange 2007 organization that is relaying messages. The Edge Transport server receives the messages for recipients in the external relay domain and then routes the messages to the e-mail system for the external relay domain. A Send connector from the Edge Transport server to the external relay domain is required in this scenario.

Where to configure Accepted Domains

                Accepted domains are configured on the Organization level, on Exchange servers that have the Hub Transport server role installed, or on servers that have the Edge Transport server role installed on them. When working with Edge servers, the best approach towards Accepted Domains would be to configure them only on the Hub Transport server role, and then populate that data on the Edge Transport server by using the Edge Subscription process. When the Edge Subscription process runs, the accepted domain configuration information is replicated to the subscribed Edge Transport server.

Note: 

To configure Accepted Domains you use must be delegated the with an Exchange Organization Administrator role. To perform the task on servers that have the Edge Transport server role installed, you must log on by using an account that is a member of the local Administrators group on that computer.

Creating Accepted Domains

As always, you can do this in one of two ways:

Using Exchange Management Console (EMC):

1. Open the Exchange Management Console. Perform one of the following steps:

On an Edge Transport server: Select Edge Transport, and then in the work pane, click the Accepted Domains tab.

On a Hub Transport server: Expand Organization Configuration, select Hub Transport, and then in the work pane, click the Accepted Domains tab.

In the action pane, click New Accepted Domain. The New Accepted Domain wizard appears.

        On the New Accepted Domain page, enter the name of the new accepted domain. Use this field to identify the accepted domain in the user interface. You can type any name that you want, but you should select a meaningful name that helps you easily identify the purpose of this accepted domain.  

 Next, enter the Accepted Domain itself. Use this field to identify the SMTP domain name for which the Exchange organization will accept e-mail messages. You can use a wildcard character to accept messages for a domain and all its sub-domains.  

Next, select one of the following options to set the accepted domain type:  

 Authoritative Domain, Internal Relay Domain, or External Relay Domain.  

Click New then on the Completion page, click Finish.

New-AcceptedDomain -Name "Petri.co.il" -DomainName petri.co.il -DomainType 

Authoritative 

To create an internal relay domain type:

New-AcceptedDomain -Name "Dpetri.net" -DomainName dpetri.net -DomainType 
InternalRelay

To create an external relay domain type:
New-AcceptedDomain -Name "Message-Pro.com" -DomainName 
message-pro.com -DomainType ExternalRelay
Changing the Default Accepted Domain
You cannot modify the default accepted domain. To change which accepted 
domain is the default accepted domain, you must create a new accepted 
domain, and then set the new accepted domain as the default by using the
 Exchange Management Shell.

If you try to remove the default accepted domain from the list without 
configuring a different default accepted domain you will get an error:
In order to find out which of the accepted domains is the default one, 
you MUST use the Management Shell (PowerShell prompt) and run the 
following command:

Get-AcceptedDomain

For example, in case you would like to totally remove the PETRI.LOCAL 
domain from the list of accepted domains, you will first need to create 
the PETRI.CO.IL accepted domain (see above example), then run the 
following command in the PowerShell prompt:

Set-AcceptedDomain -Identity petri.co.il -MakeDefault:$true
Deleting an Accepted Domain
Next, if you want to, you need to delete the old accepted domain from the list of accepted 
domains: Using Exchange Management Console (EMC):

1.Open the Exchange Management Console. Perform one of the following steps:

On an Edge Transport server: Select Edge Transport, and then in the work pane 
click the Accepted Domains tab.
On a Hub Transport server: Expand Organization Configuration, select Hub
2.Click on the accepted domain you wish to remove. In the action pane, click Remove.
3.Click Yes on the prompt.

Using Exchange Management Shell (PowerShell prompt):
Open the Exchange Management Shell prompt, then type:

Remove-AcceptedDomain –Identity petri.local