Offline attachments policy for the new Outlook for Windows

Introduction

We are introducing a new OWAMailboxPolicy setting that allows administrators to control whether file attachments are available when users work offline in the new Outlook for Windows. This change adds a tenant-level configuration option for managing offline attachment access while preserving existing offline policy behavior by default.

When this will happen:

The new policy will rollout mid-April 2026

How this affects your organization:

Who is affected:

• Exchange Online administrators
• Users of the new Outlook for Windows who use Offline mode

What will happen:

• A new OWAMailboxPolicy setting named AttachmentsOfflineEnabledWin becomes available.
• The policy is enabled by default ($true).
• Administrators can allow or block access to file attachments while working offline in the new Outlook for Windows.
• This change does not affect the existing configuration of OfflineEnabledWin.
• If OfflineEnabledWin is set to $false, offline file attachments remain disabled even if AttachmentsOfflineEnabledWin is set to $true.

What you can do to prepare:

• No action is required if the default behavior meets your organization’s requirements.
• Review your existing OfflineEnabledWin policy configuration.
• Configure AttachmentsOfflineEnabledWin at the tenant level if you want to control offline attachment access.
• Communicate any changes to helpdesk or security teams.

Learn more and configure the policy using Exchange PowerShell: Set-OwaMailboxPolicy documentation.

Compliance considerations:

No compliance considerations identified, review as appropriate for your organization.