Accepted Domains in Exchange 2016

What is Accepted Domain?

SMTP domain for which your exchange server is accepting incoming emails is known as Accepted Domain. Configuration of accepted domains is done at organizational level. Wrong configuration of accepted domain can lead to issues with mail flow in your Microsoft Exchange organization. Plan your accepted domains before modifying the configuration on Exchange server.

Types of Accepted Domains

There are 3 types of Accepted domains in Exchange 2016 as mentioned below.

  1. Authoritative
  2. Internal Relay
  3. External Relay


Authoritative Domains are those for which email messages are delivered to a recipient that has a mailbox hosted in your Exchange organization. An organization can have more than one Authoritative Domains configured. Let’s say we’ve a company named MSCloudTalks that owns a SMTP domain and users have email addresses Your exchange organization will be configured to receive emails sent to as it hosts the mailboxes of the users and the domain will be configured as an Authoritative Domain.

Authoritative domain type is the most commonly used Accepted Domain type.

Internal Relay

Internal Relay domains are those for which your exchange organization hosts some of the mailboxes and some of the mailboxes are on different system like Office 365 or Other Exchange Organization. Internal Relay domains are also referred as “Shared SMTP Namespace”. Internal Relay domains are commonly use when two companies have merged but are yet to consolidate their Exchange environment into a single organization. Exchange hybrid configuration also configured your office 365 SMTP domain as Internal Relay domain on your on premises Exchange organization.

When we’ve a need for consistent SMTP addressing across multiple exchange environments then Internal Relay domain is the best solution. When we configured accepted domain as Internal Relay, It allows exchange server to receive emails sent to the Internal Relay domain but in case if no recipient is found with the SMTP address then forward the email message to other exchange organization using Send Connector.

Let’s say we’ve a Exchange 2016 hybrid configured with office 365 and we’ve migrated 50% user mailboxes to Office 365. If a user sends an email to a user in office 365, Exchange server will first lookup for a mailbox of and if it can’t find the mailbox it will relay the email to Office 365 using Send Connector and in that case our SMTP domain will be configured as Internal Relay.

External Relay

When you would like to receive emails for SMTP domains in your exchange organization but do not host any user mailbox then in that case we configure SMTP domain as External Relay. External Relay domains are those for which an Exchange organization will accept email, but doesn’t hosts any mailbox.

Externally Relay domains are usually configured on ISP side when ISP is providing anti-spam/antivirus services to email services of other organization. Email from the internet hits the ISP server and ISP server perform spam,antivirus checks and forwards the email to exchange organization that hosts the mailboxes of the SMTP domain.

Prerequisites for Accepted Domains

 Following prerequisites needs to be fulfilled before configuring any SMTP domain as accepted domain in your exchange organization.
  • Accepted domain isn’t configured as Remote Domain in Exchange Server. Let’s say if you’ve configured as Remote Domain then you can’t add as Accepted Domain.
  • Make sure you own the SMTP domain before configuring accepted domain, verify that public DNS MX record for SMTP domain exists and its pointing to a server in your Exchange organization.

Changes in Accepted Domains are done at the organization level and the impact will be on complete Exchange Organization. You need to have Organization Management rights to work with Accepted Domains in Exchange 2016.

Once you verify these prerequisites for Accepted Domains are fulfilled then go ahead and configure Accepted Domains.

Configuring Accepted Domains in Exchange 2016

  • To configure Accepted Domains in Exchange 2016, Login to Exchange Admin Center using Organization Management account
  • Navigate to EAC > Mail Flow > accepted domains

Accepted Domains in Exchange 2016

  • Click on + icon to add an Accepted domain

Accepted Domains in Exchange 2016


  • Enter the name, accepted domain and select the domain type and hit Save.

Accepted Domains in Exchange 2016

If you’ve Edge Server configured then you don’t have to perform these steps on Edge Server, changes will be replicated to Edge server next time when the EdgeSync synchronization occurs.

  • Once the accepted domain is added to your exchange organization, verify the domain type and mail flow to and from the SMTP domain.

Accepted Domains in Exchange 2016

To add an Accepted Domain using EMS. Run the following EMS cmdlet.

New-AcceptedDomain -DomainName -DomainType Authoritative -Name CloudTalks