MC1125491 - Microsoft Outlook for Windows: Add attachments while offline

Updated August 27, 2025: We have updated the timeline. Thank you for your patience.

Introduction

We’re enhancing offline functionality in the new Microsoft Outlook for Windows. This update (Microsoft 365 Roadmap ID 496371) enables users to add file attachments while composing emails offline, improving productivity for those working without an internet connection.

When this will happen

• Targeted Release (Worldwide): Rollout begins in mid-September 2025 and is expected to complete by mid-October 2025.
• General Availability (Worldwide): Rollout begins in mid-November 2025 and is expected to complete by late November 2025.
• General Availability (GCC): Rollout begins in early December 2025 and is expected to complete by mid-December 2025.

How this affects your organization

Users with offline mode enabled in the new Outlook for Windows will be able to attach files to draft emails while offline. These emails, including attachments, will be sent automatically once the device reconnects to the internet.

This feature will be on or off by default based on your current configuration of the OWAMailboxPolicy-OfflineEnabledWin policy. No changes will be made to existing configurations.

What you can do to prepare

To enable this functionality, ensure the following settings are configured in the new Outlook under Settings > General > Offline:

• Enable offline email, calendar, and people
• Include file attachments

Admins can manage this feature using the OWAMailboxPolicy-OfflineEnabledWin mailbox policy. Learn more at Set-OwaMailboxPolicy.

Caption i. Offline editing can be enabled or disabled in Settings > General > Offline

Compliance considerations

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