Missing Subfolders

Question

My subfolders are missing all of a sudden. If I login to my account again on my Mac, I'm afraid I'll lose the folders forever. How an I backup to an earlier version of my .ost file?

Answer 1

Hi Steven Brown,

I understand how concerning it is to see subfolders disappear suddenly, especially when you are worried that signing in on another device could make the situation permanent. Please note that this is a user-to-user forum, so contributors can share troubleshooting steps but do not have access to your account or server-side data.

The Q&A Assist answer is on the right track that an .ost file is not a point-in-time backup you can reliably “roll back.” Have you had a chance to try the webmail check mentioned there (to confirm whether the folders still exist online)? If you can share what you see online, it will immediately narrow down the correct recovery path.

Since you had Windows / Classic Outlook tags but also mentioned using a Mac, could you clarify which app you are using when you notice the missing subfolders?

This matters because .ost files are a Windows Outlook data file concept, and the safest next step depends on whether the folders are missing in the mailbox itself (web) or only missing in one specific client.

In addition to what Q&A Assist already covered, here are a few extra checks

1. If the missing folders were created under a local-only area (for example, local archives or “on this computer” type folders), they will not sync to other devices and may not appear on the Mac at all. In that situation, the focus should be on the Windows Outlook profile where they were created, rather than signing in elsewhere.
2. If the folders are not visible in Deleted Items, it is still worth checking whether they are recoverable (depending on account type). Outlook can sometimes restore items that are no longer in Deleted Items via the recover/recoverable options in Classic Outlook. Recover and restore deleted items in Outlook - Microsoft Support 
3. If you suspect the local data file view is not displaying correctly or the local cache is out of sync, Microsoft’s guidance for data-file related issues is to use supported repair and rebuild approaches rather than trying to revert the .ost to an older state. Repair Outlook Data Files (.pst and .ost) - Microsoft Support 

If you reply with just two details, the next step becomes much clearer:

• Do you see the missing folders when you sign in on the web (Outlook on the web)?
• Are these folders part of the mailbox folder tree, or were they created in a local-only area inside Outlook on Windows?

I hope this helps you narrow down the safest recovery approach before making any changes.

---

Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.  

Answer 2

Outlook does not support “backing up to” or rolling back an .ost file to an earlier version. An .ost (Offline Outlook Data File) is just a local cache of what is stored on the mail server; it is not a primary backup. If subfolders disappeared because they were removed or changed on the server, the .ost will simply mirror that state.

To protect or recover data, use these supported approaches instead:

1. Check server mailbox and resync

• If the account is Exchange/Outlook.com/Microsoft 365, sign in via webmail and verify whether the subfolders still exist there.
• If they do, force a resynchronization in Outlook by using Send/Receive → Update Folder or Send/Receive All Folders.
• If synchronization is failing or the .ost is damaged, create a new .ost file and resync all folders as described in the guidance for damaged .ost files: create a new .ost and then synchronize the offline folders again.

2. Use a .pst file for backup/restore

• For backup going forward, export the mailbox (including subfolders) to a .pst file. When exporting, ensure Include subfolders is checked so that all subfolders are captured.
• If a .pst backup already exists from before the folders went missing, import that .pst into Outlook and recover the missing folders/items from there. When importing, Outlook copies the data into the current mailbox or data file.

3. If the .ost/.pst is corrupted

• If data loss is due to file corruption, use the Inbox Repair Tool (ScanPST) on the .pst file and then recover items into a new Outlook Data File as described in the repair guidance. For .ost issues, the supported method is to rebuild the .ost and resync from the server rather than trying to roll it back.

There is no supported method to revert an .ost to an earlier point in time; recovery must come from the server copy, a .pst backup, or repaired data files.

---

References:

• Issues when you synchronize your Exchange Server mailbox with your .ost file in Outlook
• Fix problems importing an Outlook .pst file
• Repair Outlook Data Files (.pst and .ost)
• How do I recover my old email messages, my contacts and everything else I had in Outlook? - Microsoft Q&A