Conditional access and Outlook on the web for Exchange Online

This week a blog post about conditional access. More specifically, about conditional access and enforced restrictions with Outlook on the web for Exchange Online. This can be used to provide users with access to Outlook on the web, but still protect company data. That can be achieved by configuring a limited experience for users with regards to attachments. The enforced restrictions can enable a read only option for attachments in the browser and can completely block attachments in the browser. In this post I’ll walk through the required configurations, with the focus on conditional access, and I’ll show the end-user experience.

Configuration

Let’s start with looking at the configuration. The main focus in the configuration is conditional access, but as that configuration has no use without configuring the Outlook on the web mailbox policies, I’ll also provide the main configuration options from an Exchange Online perspective.

Exchange Online configuration

The most important and only configuration, from an Exchange Online perspective, is to configure the Outlook on the web mailbox policy. That configuration must be done by using PowerShell. When there is an Outlook on the web mailbox policy, the required cmdlet is Set-OwaMailboxPolicy. That cmdlet contains the parameter ConditionalAccessPolicy. That parameter can be used to specify the Outlook on the web mailbox policy for limited access and can have the following values:

• Off: This value means that no conditional access policy is applied to Outlook on the web;
• ReadOnly: This value means that users can’t download attachments to their local computer, and can’t enable offline mode on non-compliant computers;
• ReadOnlyPlusAttachmentsBlocked: This value means that all restrictions from ReadOnly apply, but that users can’t view attachments in the browser.

Note: In the end-user experience section, I’ll show the experience for both values.

Conditional access configuration

Once the conditional access policy configuration is in place for the Outlook on the web mailbox policy, it’s time to look at the actual conditional access configuration in Azure AD. The following eight steps walk through the steps to create a conditional access policy that will require multi-factor authentication and enforce a restriction on Outlook on the web, for devices that are not hybrid Azure AD joined and that are not compliant.

End-user experience

Let’s end this post by looking at the end-user experience, for both configurable values for the Outlook on the web mailbox policy for limited access. When using an unmanaged device the user must user multi-factor authentication, which will be followed by the experiences showed below.

The first value is the ReadOnly value, which forces read only restrictions to any email attachment. Besides that it also prevents users from saving the attachments locally, as it only allows the user to save the attachments to OneDrive. Below is an example of that behavior. It also shows on top of the mail that the user is notified about the limited experience.

The second value is the ReadOnlyPlusAttachmentsBlocked value, which forces email attachments to be blocked from being opened via Outlook on the web. Basically it prevents any interaction with the attachment. Below is an example of that behavior. It also shows on top of the mail that the user is notified about the limited experience.

Note: This behavior does require disciplined users, as these type of limitations in the user experience might trigger users to forward messages to another account.

More information

For more information about conditional access in combination with Outlook on the web for Exchange Online, please refer to the following articles:

• What are access controls in Azure Active Directory conditional access?: https://docs.microsoft.com/en-us/azure/active-directory/conditional-access/controls#session-controls
• Conditional Access in Outlook on the web for Exchange Online: https://techcommunity.microsoft.com/t5/Outlook-Blog/Conditional-Access-in-Outlook-on-the-web-for-Exchange-Online/ba-p/267069
• Set-OwaMailboxPolicy: https://docs.microsoft.com/en-us/powershell/module/exchange/client-access/set-owamailboxpolicy?view=exchange-ps
• Connect to Exchange Online PowerShell using multi-factor authentication: https://docs.microsoft.com/en-us/powershell/exchange/exchange-online/connect-to-exchange-online-powershell/mfa-connect-to-exchange-online-powershell?view=exchange-ps