This article talks about the importance of configuring Exchange Remote Domain, both on Exchange on-premise and Exchange Online, to control the format and type of email messages exchanged between hosted mailbox users and on-premise mailbox users.
What is Exchange Remote Domain?
It is a feature in Microsoft Exchange that allows IT Admins to control both the type and format of emails exchanged with external remote domains.
Suppose we are dealing a lot with contoso.com company, and we want them to see our internal Out Of Office OOF messages, and not the external ones. Well, we can configure that domain as a remote domain in Exchange, and configure that remote domain Set-RemoteDomain so that Exchange will send the internal OOF message and not the external one for that remote domain.
Moreover, suppose that your company don’t want people to auto forward emails to external domains. If your company cares about a specific partner like xyz.com domain, then you can configure a remote domain for xyz.com, and allow forwarding emails only to that domain.
By default, there is a default remote domain in each Exchange organization called (*). It controls how we, as Exchange organization, deal with all external domains to which there is no specific remote domain defined.
Things become interesting when you are migrating to Office 365 and you are in a hybrid mode. You will have to domains to care about (contoso.onmicrosoft.com, and contoso.mail.onmicrosoft.com). Since those domains are related to your Office 365 environment, you should consider them trusted, and treat mailboxes in Office 365 the same way you treat your on-premise internal mailboxes. This is where remote domains might help.
So, we shall create two remote domains in our Exchange on-premise setup for Office 365 domains, and relax the settings, like allowing forwarding emails, showing the internal Out Of Office message, and also enable the “voting buttons” by enabling a feature called TNEFE (Transport Neutral Encapsulation Format). From the other side, we shall do the same. In Exchange Online we shall create a remote domain for contoso.com and relax the settings.
Usually the Hybrid configuration wizard will create a remote domain on our Exchange on-premise for contoso.mail.onmicrosoft.com, so we only need to create a remote domain in Exchange on premise for contoso.onmicrosoft.com in addition.
New-RemoteDomain -Name "Hybrid Domain - contoso.onmicrosoft.com" -DomainName contoso.onmicrosoft.com
Also, we need to update the SMTP outbound connector [ the connector for emails going to Office 365 name space] from our Exchange on-premise to include contoso.onmicrsooft.com in addition to contoso.onmicrosoft.com.
Let us configure the remote domains using Set-RemoteDomain to match the following configuration:
Finally, we need to use Set-RemoteDomain to configure both contoso.onmicrosoft.com and contoso.mail.onmicrosoft.com remote domains as shown in the below figure:
Now going to Exchange Online, we shall create remote domain for contoso.com with similar configuration.
The most important settings are to consider are listed below. Make sure you match the settings in the previous figure with what you have:
It is so important to make sure your Office 365 users and on-premise users do not feel any difference when exchanging emails. To them, they have a corporate mailbox, and it does not matter to them whether the mailbox is hosted in Office 365 or on-premise mailbox. To do that, you need to carefully configure Exchange remote domains as explained in this blog post.