One day, I got a message from a Mastodon follower. They said attachments sent through Outlook.com were being saved in OneDrive—without them realizing it. Weird, right? I dug into it and found that Microsoft announced something big on March 5, 2025: starting this month, Microsoft 365 will use OneDrive for storing files and folders. This change is tied to a feature called Known Folder Move (KFM). Let’s break it down.
Table of Contents
Reader Observations: Attachments in OneDrive
The Mastodon user noticed that attachments sent through Outlook.com were “accidentally” ending up in their OneDrive storage. If true, this could be problematic. Why?
- Privacy Risk: If your OneDrive settings allow public access, anyone might retrieve those attachments.
- Storage Quota: Attachments saved in OneDrive count toward your storage limit, which could lead to unexpected costs or limitations.
Another reader commented that this behavior isn’t new—it’s been happening since 2015. Attachments have been auto-saved to OneDrive for years now, and for the past three years, they’ve even been counted against your storage quota. You can verify this by checking your account settings under “Account > Storage” on Outlook.com.
My Test Results
I decided to test this myself. I sent an email with a small attachment via Outlook.com and Thunderbird. Nothing unusual happened—no duplicate emails, no mysterious file saving. Maybe my attachment was too small? Or maybe this issue only happens sporadically or with larger files? If you’ve experienced this, let me know.
Precautionary Measures
Here’s what you can do to protect yourself:
- Check Your OneDrive Settings: Ensure your cloud storage isn’t accessible to strangers.
- Audit Your Files: Regularly inspect your OneDrive account and delete sensitive documents that shouldn’t be stored there.
- Monitor Storage Usage: Keep an eye on how much space your attachments are using in OneDrive.
Microsoft 365’s Shift to OneDrive (KFM)
From March 2025 onward, Microsoft 365 apps like Word, Excel, and PowerPoint will prompt users to back up files to OneDrive using Known Folder Move (KFM). Here’s how it works:
- Prompted Backup: A message bar will appear in desktop apps encouraging users to save files to OneDrive.
- Folder Selection: You choose which folders to back up—no admin intervention needed.
- Global Rollout Timeline: Preview starts mid-March 2025; full rollout finishes by early May 2025.
Once activated, KFM automatically syncs files to the cloud while keeping them accessible through File Explorer or the OneDrive app.
Benefits of KFM
Microsoft highlights several advantages of using KFM for file storage:
- Copilot Integration: Files are optimized for AI tools like Copilot for enhanced productivity.
- Collaboration: Share files easily, add comments, and enjoy AutoSave for seamless teamwork.
- Remote Access: Access files from anywhere—Windows, Mac, web browsers, iOS, or Android devices.
- Security & Compliance: Files are protected by organizational policies like Classification, Labeling, and Protection (CLP).
- Backup Protection: Prevent data loss due to device failures or accidents.
The Downsides
While KFM offers plenty of perks, there are potential drawbacks:
- Cloud Dependency: If the cloud service goes down or gets hacked, access could be disrupted.
- Privacy Concerns: Misconfigured settings might expose sensitive data to unauthorized users.
Administrators need to evaluate whether blocking KFM is necessary for their organization.
This shift toward cloud-based storage is a double-edged sword—offering convenience and security while raising concerns about privacy and dependency on external services. Take proactive steps to secure your data and understand how these changes impact your workflow.