Outlook creates a handful of local files to make offline access and synchronization work. Among them are .nst files—commonly referred to as Offline Storage Table files.
If you’ve been told to delete an NST file to fix sync errors, duplicate offline folders, or odd performance issues, you probably want a clear, safe answer: can you delete it, and what will it break?
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This guide explains what Outlook NST files do, when deletion is safe, and the exact Windows steps to remove them without risking your actual mailbox data.
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An NST file (Offline Storage Table) is a local cache/index structure Outlook uses to support offline folders and synchronization. It helps Outlook track what was downloaded, what changed, and how to represent offline content.
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NST files aren’t your mailbox. They’re local state that Outlook uses to speed up and manage offline access. If the file becomes corrupted or out of sync, Outlook can behave oddly—errors on send/receive, broken offline views, or repeated resync cycles.
Can you delete Outlook NST files?
Yes, in many situations you can delete Outlook NST files. When you delete an NST file while Outlook is fully closed, Outlook typically recreates what it needs the next time it starts and resynchronizes.
That said, whether deletion will fix your problem depends on the root cause. In most practical cases, removing NST files clears corrupted local offline state without deleting emails from the server.
What happens after deletion
Deleting NST files usually results in a resync/rebuild of offline folder state. You should expect these outcomes:
- Local offline organization may reset (for example, offline folders may re-download).
- Outlook may rebuild indexing/caches, which can temporarily slow startup.
- Your mailbox content remains on the server (Exchange/Microsoft 365/IMAP/POP source), assuming the account still exists and sync is working.
- If you rely on offline-only copies, you might see a brief period where offline content isn’t immediately available until resync finishes.
If your issue is a corrupt cache rather than a server-side problem, NST deletion can be an effective fix.
Prerequisites before you delete
Before deleting anything, do these checks to avoid unnecessary risk:
- Fully close Outlook. Don’t just minimize—verify it’s not running.
- Open Task Manager and end
OUTLOOK.EXEif present. - Decide whether you’re troubleshooting a single account or multiple. NST locations can vary depending on Outlook version and account type.
- If you want a safety net, rename NST files instead of deleting them.
Renaming (e.g., adding .bak) lets you restore quickly if Outlook doesn’t behave as expected.
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Method 1: Delete NST files manually (recommended for most cases)
This method is straightforward: close Outlook, locate NST files, remove (or rename) them, then restart Outlook and let it rebuild offline state.
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Step-by-step: locate NST files
On Windows, NST files are commonly stored under your Outlook profile and local application data. Use File Explorer search to find them quickly.
- Press Win + E to open File Explorer.
- In the address bar, paste one of these paths (start with the first):
%localappdata%\Microsoft\Outlook%appdata%\Microsoft\Outlook
- Use the search box in File Explorer and search for
.nst. - If search returns nothing, expand your search to the whole user profile for
*.nst(it can take time).
Look for file names that look like Outlook internal offline folder/cache files. The exact name varies by version and profile.
Step-by-step: delete (or rename) NST files
- Keep Outlook closed (again: confirm
OUTLOOK.EXEis not running). - In the folder where you found
.nstfiles, sort by Date modified if you want to focus on recent files. - Rename first (safer): right-click an NST file → Rename → append
.bak. - If you’re confident, delete the NST file(s) instead. Use Delete or Shift + Delete.
- Repeat for any other NST files you found in the same location.
If you have multiple Outlook profiles on the same machine, ensure you’re targeting the profile you actually use.
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Step-by-step: verify Outlook rebuilds them
- Start Outlook.
- Wait for it to connect and synchronize. Depending on mailbox size and network speed, this can take minutes to longer.
- Check whether Outlook completes folder updates (you may see a progress bar or activity in the Send/Receive status).
- After some time, return to the NST file location and verify new
.nstfiles appear (or renamed.bakfiles remain untouched).
If Outlook never recreates them, that usually means the offline cache feature/account type isn’t using NST files in your setup—or Outlook is failing earlier due to a larger profile issue.
Method 2: Reset Outlook offline/cache state (when NST won’t rebuild)
If deleting NST files doesn’t restore normal behavior, the local cache reset may need to go further. The goal is to rebuild Outlook state without touching your mailbox on the server.
Clear the offline file caches you can control
Depending on your Outlook version and account type, you may also have related local cache files (for example, offline folders data, address book caches, or search indexes). Be selective: remove caches you know are safe, and keep a backup if you’re unsure.
Common safe approach: rename/delete the specific problematic .nst files (your primary change), then allow Outlook to rebuild. If that fails, proceed to profile-level repair steps below.
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Rebuilding the profile is often the point where stubborn offline cache issues stop being “file-level” and become “configuration-level.”
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- Close Outlook.
- Open Control Panel → Mail (or search Start for Mail).
- Select Show Profiles.
- Create a new profile and add your account again (Exchange/Microsoft 365/IMAP).
- Set the new profile as the default.
- Start Outlook using the new profile and let it resynchronize.
Rebuilding profiles doesn’t erase mailbox content on the server. It does reset client-side configuration and can trigger new cache builds (including offline storage files).
Common causes of NST problems
Most NST corruption issues come from incomplete shutdowns, synchronization interruptions, or disk issues. Typical triggers include:
- Outlook crash or forced shutdown (power loss, app kill, OS update interruptions).
- Network instability during offline synchronization.
- Large mailbox changes (migration, mailbox moves, permission updates).
- Disk errors or storage performance problems on the drive holding your local Outlook data.
- Multiple Outlook instances connected to the same profile unexpectedly.
If you suspect recurring corruption, focus on stability: stable power/network, correct Windows updates, and healthy disk health.
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These details are where most people accidentally cause bigger problems:
- Don’t delete OST/PST files unless you’re sure what you’re doing. NST files are typically safer to remove than the primary mailbox data containers.
- Close Outlook completely before deleting. If Outlook is running, it can recreate or lock files mid-change.
- Rename first if you’re not sure which NST file belongs to which account/profile.
- Account type matters. Exchange/Microsoft 365 cached mode uses OST; offline folder behavior differs depending on protocol and Outlook build.
- Expect resync time. If you delete multiple caches at once, Outlook can take longer to settle.
Troubleshooting: what to try when deletion doesn’t fix it
If removing NST files doesn’t resolve your issue, treat it like a diagnostic sequence. Start small and move toward broader repairs only if needed.
1) Confirm you closed the correct Outlook process
Sometimes Outlook “looks closed” but OUTLOOK.EXE keeps running in the background. Re-check Task Manager after you close it.
2) Try renaming instead of deleting
If you deleted the file and things got worse, restore the renamed/backup version (remove .bak) and try again with a narrower scope.
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If you have multiple mail profiles, you may have deleted NST files for a profile you aren’t using. Verify the active profile and then locate NST files under that user context.
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4) Rebuild the Outlook data file state (ScanPST for PST; repair for others)
If your problem involves PST corruption (typically with older setups or IMAP/POP configurations using PST), use the inbox repair tool. For PST, Microsoft ships ScanPST.exe. Search your Outlook install folder for it and follow Microsoft’s guidance.
If you’re on Exchange cached mode, focus on profile/offline cache issues rather than PST repair.
5) Repair Microsoft 365/Office installation
For repeated client-side failures, run Office repair from Windows Settings (Apps → Installed apps → Microsoft 365/Office → Modify → choose Online Repair or Quick Repair depending on what’s available).
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NST vs OST vs OAB: don’t delete the wrong thing
Outlook uses several local file types. Only remove the one tied to your problem.
| File type | Typical purpose | Usually safe to delete? | Main risk |
|---|---|---|---|
| .nst | Offline Storage Table / local offline state | Often yes (Outlook can recreate) | Offline cache resync delay; offline view resets |
| .ost | Cached copy of mailbox in Exchange cached mode | Sometimes (if you re-sync), but higher impact | Long re-download; can appear like data loss while syncing |
| .pst | Personal storage file (local mail archive) | No, not unless you’re sure | Actual mailbox data could be removed |
| .oab (Offline Address Book) | Address book cache | Often yes to rebuild | Address book update delay; free/busy issues until rebuilt |
If your goal is to fix offline sync oddities, NST deletion is usually the lower-risk first move compared with nuking an OST or PST.
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Sometimes you can avoid deletion entirely by resetting Outlook’s offline behavior through built-in controls.
Disable and re-enable offline cache features
If your problem is offline-related (e.g., folder sync oddities), toggling offline behavior can force a refresh without manual file deletion. The exact switches depend on your Outlook version and account type.
Force a resync
Use Outlook’s normal sync triggers (Send/Receive). Let it fully complete before judging results.
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Repair the Outlook profile configuration
If NST deletion doesn’t rebuild state, profile-level fixes (as described in Method 2) can address deeper misconfiguration.
FAQs about deleting Outlook NST files
Will deleting NST files delete my emails?
No. NST files are local offline state (cache/index). Your emails live in your mailbox on the server (Exchange/Microsoft 365/IMAP/POP source). After deletion, Outlook may re-download offline content.
Do I need to delete NST files for every Outlook account?
Only if you’re troubleshooting a specific account/profile where the NST files are used. If you have multiple profiles, locate NST files within the correct profile context first.
How long does it take for Outlook to recreate NST files?
It varies. Small mailboxes may rebuild quickly (often within minutes). Large mailboxes or unstable networks can take longer, especially if Outlook needs to resync folder state.
What if Outlook keeps recreating the NST file immediately, but the issue persists?
That usually points to a recurring underlying problem—profile misconfiguration, permission issues, network instability, or a broader Outlook cache/index issue. In that case, move to profile rebuild or Office repair rather than repeatedly deleting NST files.
Where exactly are NST files stored?
Most commonly under your user profile in paths like %localappdata%\Microsoft\Outlook. The precise folder can change with Outlook version and profile setup, so use .nst search to confirm the actual location.
Bottom Line
In most real-world troubleshooting cases, you can delete Outlook NST files safely—provided Outlook is fully closed—because NST files are local offline state that Outlook typically recreates. The trade-off is usually a resync delay and refreshed offline folder organization.
If deletion doesn’t help, treat it as a sign the problem is deeper than a single corrupted cache file. Move toward profile rebuild and client repair steps, and avoid deleting OST/PST unless you’re intentionally reinitializing cached data with a clear plan.
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