Simplify the Outlook Web App URL for Microsoft 365 or Office 365 Hybrid

Learn how to configure a URL for Outlook on the web (Outlook Web App) for cloud mailbox users in a hybrid environment.

A major concern for organizations that move to Microsoft 365 or Office 365 from on-premises Exchange is the user experience. Users need uninterrupted access to their mailboxes regardless of where or when their mailbox is moved. With that in mind, the Outlook on the web (formerly known as Outlook Web App) coexistence story is important.

Consider the following scenario: a company uses a hybrid deployment to move some of their mailboxes from on-premises Exchange to Microsoft 365 or Office 365. On Friday before the move, the users accessed their on-premises mailboxes by using the URL https://mail.contoso.com/owa. On Monday after the move, those same users now get an error when they try to access their mailboxes by using that URL.

To allow the affected users to connect to their mailboxes by using Outlook on the web, you have two options:

• Tell the users the new URL (for example, https://outlook.com/owa/contoso.com): The issues with this option are:

  • The URL is complex.

  • The experience isn't seamless for the affected users.

• Configure the TargetOWAUrl setting on the organization relationship: The issues with this option are:

  • The endpoint for the cloud mailboxes is external (it's not in the domain that users expect).

  • The endpoint requires the domain in the URL (to distinguish between Microsoft 365 Apps for business and outlook.com consumer offerings).

  • The endpoint causes users to see certificate mismatch warnings.

To eliminate these issues for users with cloud mailboxes, perform the following steps:

1. Create a CNAME record in DNS (for example, cloudowa.contoso.com) that points to mail.office365.com:

   • Be sure to create this CNAME record in your internal and external (public) DNS, because users might connect from internal or external Internet connections.

   • In our example, the domain contoso.com is used in the request (the cloudowa part is dropped). This means you don't need to specify the domain in the URL.

2. Configure the Outlook on the web redirect in the on-premises organization relationship: To do this, use the following syntax in the Exchange Management Shell in on-premises Exchange:

   Set-OrganizationRelationship -Identity <Organization relationship identity> -TargetOWAUrl http://<CNAME value>/owa
   

   For example, if the CNAME record that you created in Step 1 is cloudowa.contoso.com, and the organization relationship name is Contoso Cloud, run the following command:

   Set-OrganizationRelationship -Identity "Contoso Cloud" -TargetOWAUrl http://cloudowa.contoso.com/owa
   

   Note

   • Use http, not https. If https is used, users may get a URL redirection issue [AADSTS50011].

   • The trailing value /owa is required in the organization relationship, but users don't need to enter /owa in the URL.

   • You can use the Get-OrganizationRelationship cmdlet to find the organization relationship name.

After you apply this setting, the users can continue using the current Outlook on the web URL to access their on-premises mailboxes. In the previous example, the value is https://mail.contoso.com/owa.

Multiple authentication prompts

Users may receive multiple authentication prompts depending on:

• Where they connect from (internal or external Internet connections).

• If their computer is or isn't domain joined.

• If you're using identity federation in your hybrid environment.

The authentication prompt experience that users can expect is described in the following table.