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As an admin, you can set up both private and public attachment handling in Outlook on the web (formerly known as Outlook Web App) depending on how you configure your Outlook on the web mailbox policies. The settings for private (internal) and public (external) networks define how users can open, view, send, or receive attachments depending on whether a user is signed in to Outlook on the web on a computer that is part of a private or of a public network.
Although there are both private (internal network) and public (external network) settings to control attachments using Outlook on the web mailbox policies, admins require more consistent and reliable attachment handling when a user signs in to Outlook on the web from a computer on a public network such as at a coffee shop or library. To set up the ability to enforce attachment handling from external networks for an entire organization in Exchange Online, first use the Set-OrganizationConfig cmdlet, set the PublicComputersDetectionEnabled parameter to $true, configure the correct Outlook on the web mailbox policy either by using the Exchange admin center (EAC) or the Set-OwaMailboxPolicy cmdlet and create claim rules in AD FS. Enabling this setting on the Set-OrganizationConfig cmdlet and creating the claim rules enable Exchange Online to tell if a user is signing in to Outlook on the web from a private and public network or computer.
The Outlook on the web mailbox policy parameters in the following table should be set to $true to enable an admin to control attachment handling for public computers and networks.
| Parameter* | Description |
|---|---|
| DirectFileAccessOnPublicComputersEnabled | Specifies left-click and other options available for attachments when the user has signed in to Outlook on the web from a computer outside of a private or corporate network. If this parameter is set to $true, Open and other options are available. If it's set to $false, the Open option is disabled. |
| ForceWacViewingFirstOnPublicComputers | Specifies whether a user who signed in to Outlook on the web from a computer outside of a private or corporate network can open an Office file directly without first viewing it as a webpage. |
| WacViewingOnPublicComputersEnabled | Specifies whether a user who has signed in to Outlook on the web from a computer outside of the corporate network can view supported Office files using Outlook on the web. |
Procedures in this topic require specific permissions. See each procedure for information related to each procedure's permissions.
Enable Outlook on the web on a user's mailbox if it has been disabled.
Verify that cookies have been enabled in the Web browser for all the users in your organization.
Set up and configure single sign-on (SSO) using AD FS:
For information about how to use Windows PowerShell to connect to Exchange Online, see Connect to Exchange Online PowerShell.
For information about keyboard shortcuts that may apply to the procedures in this article, see Keyboard shortcuts for the Exchange admin center.
Run the following command:
Set-OrganizationConfig -PublicComputersDetectionEnabled $true
Note
Setting this parameter to $true won't affect the settings for the following parameters:
You must create a custom claim rule because an AD FS server relies on the presence of the x-ms-proxy claim to detect whether user is coming from an internal or external network. When an AD FS proxy is deployed for external or public access, and if the user is coming from outside a private network, there's a x-ms-proxy claim sent from AD FS proxy to an AD FS server. For more information about claim rules in AD FS, see Create a Rule to Send Claims Using a Custom Rule.
On the Start Screen, type AD FS Management, and then press Enter.
In AD FS console tree, go to AD FS\Trust Relationships > Relying Party Trusts and select O365 Identity Platform.
In O365 Identity Platform, select Edit Claim Rules > Add Rule > Issuance Transform Rules.
On the Select Rule Template page, under Claim rule template, select Send Claims Using a Custom Rule from the list, and then select Next.
On the Configure Rule page under Claim rule name, type the display name for this rule.
Under Custom rule, input the following text:
exists ([Type == "http://schemas.microsoft.com/2012/01/requestcontext/claims/x-ms-proxy"]) => issue(Type = "http://schemas.microsoft.com/ws/2012/01/insidecorporatenetwork", Value = "false");
Next, input the following text:
NOT exists ([Type == "http://schemas.microsoft.com/2012/01/requestcontext/claims/x-ms-proxy"]) => issue(Type = "http://schemas.microsoft.com/ws/2012/01/insidecorporatenetwork", Value = "true");
Select Finish.
In the Edit Claim Rules dialog box, select OK to save the rule.
In the EAC, select Roles > Outlook web app policies. Or, use Outlook web app policies.
Select the mailbox policy by clicking anywhere in the row other than the button option that appears in the blank area next to the Name column.
In the Details flyout that opens, select Manage access.
Under File access, select how users can view and access attachments from public or private computers:
Select Save changes to update the policy.
Run the following command:
Set-OwaMailboxPolicy -Identity MyOWAPublicPolicy -DirectFileAccessOnPublicComputersEnabled $true -ForceWacViewingFirstOnPublicComputers $true -WacViewingOnPublicComputersEnabled $true
An attachment can be a file that's created in any program, for example, a Word document, an Excel spreadsheet, a .wav file, or a bitmap file. Users can attach or include one or more files on any item that they create in their mailbox, for example, an email message, calendar item, or contact. Outlook on the web allows you to send and receive many common files types continuously.
Some attachments might be removed or blocked by an antivirus software used by your organization, by the organization of the recipients of your email, or you might be required to save them on your computer before you can open them. By default, Outlook on the web allows you to open attached Word, Excel, PowerPoint, text files and many media files directly. The files you can open from Outlook on the web vary depending on your account settings. The following list describes the default file name extensions that you can open in Outlook on the web.
File name extensions allowed by default:
Training
Module
Manage Safe Attachments - Training
This module examines how to manage Safe Attachments in your Microsoft 365 tenant by creating and configuring policies and using transport rules to disable a policy from taking effect in certain scenarios. MS-102
Certification
Microsoft Office Specialist: Outlook Associate (Office 2019) - Certifications
Demonstrate that you have the skills needed to get the most out of Outlook 2019 by earning the Microsoft Office Specialist (MOS) certification.