Fix Outlook Error 0x80040600 on Windows 10

Outlook error 0x80040600 on Windows 10 usually means your mailbox file (.pst or .ost) has hit its size limit or is corrupted, and the fix is to reduce the file size or repair it with the built-in Inbox Repair tool. This error typically appears when you try to send or receive email, and it often comes with a message like “Unknown Error 0x80040600.” Below we explain what causes it and walk you through the fixes that work for most people.

What Causes Outlook Error 0x80040600?

Error 0x80040600 is a MAPI (Messaging API) error that Outlook throws when it cannot write to your local data file. The most common triggers are:

PST file size limit exceeded: Classic Outlook (non-Microsoft 365) has a 20 GB limit for PST files. Once you hit it, send/receive fails with this error.
OST file corruption: If you use an Exchange, Microsoft 365, or IMAP account, the offline cache (OST) can get corrupted after a crash or improper shutdown.
File permissions: Windows may have changed permissions on the Outlook data folder, preventing Outlook from writing.
Antivirus interference: Some security software locks or scans PST files mid-operation, causing the error.
Add-ins: A faulty add-in can trigger this error during mail operations.

Before You Start: Back Up Your Data

Repairing or compacting a data file is safe, but it is wise to back up your PST first. In Outlook, go to File > Account Settings > Account Settings, then the Data Files tab. Note the location of your PST file, close Outlook, and copy that file to a USB drive or another folder. If anything goes wrong, you can restore it.

Fix 1: Run the Inbox Repair Tool (ScanPST.exe)

Outlook includes a built-in repair utility for PST files. It fixes corruption that often causes error 0x80040600.

Close Outlook.
Navigate to the ScanPST.exe location. For 64-bit Outlook on Windows 10, it is usually:
C:\Program Files\Microsoft Office\root\Office16\ScanPST.exe
For 32-bit Outlook, it is in C:\Program Files (x86)\Microsoft Office\root\Office16\. The exact folder may vary (Office15 for 2013, Office16 for 2016/2019/365).
Run ScanPST.exe, click Browse, and select your PST file.
Click Start. If it finds errors, check Make a backup of scanned file before repairing, then click Repair.
After it finishes, restart Outlook and try sending/receiving.

If the error persists, the file may be too large, which leads to the next fix.

Fix 2: Reduce the Size of Your PST File

If you are near the 20 GB limit, compacting or archiving will free up space. Here is how:

Compact the PST: In Outlook, go to File > Account Settings > Account Settings > Data Files. Select your account, click Settings, then Compact Now. This removes empty space but does not delete any emails.
Archive old items: Use File > Cleanup Tools > Archive. Choose a date older than one year and archive to a separate PST. This moves items out of your main file.
Delete large attachments: Use the search bar to find messages with attachments (e.g., hasattachments:yes), then delete or save them elsewhere.

After compacting, restart Outlook. If the error was due to size, it should be gone.

Fix 3: Recreate the OST File (for Exchange/IMAP Accounts)

If you use an Exchange, Microsoft 365, or IMAP account, the OST file can be rebuilt from the server. This is often the fastest fix for 0x80040600.

Close Outlook.
Open Control Panel > Mail (or search for “Mail” in Windows).
Click Email Accounts, select your account, and click Change.
In the Offline Settings section, uncheck Use Cached Exchange Mode (or set the slider to All). Click Next, then Finish.
Restart Outlook. It will create a new OST file and download your mail from the server.

If you cannot change the setting, you can simply delete the OST file (it will be recreated). To find it, go to File > Account Settings > Account Settings > Data Files, note the path, close Outlook, and delete the .ost file. Outlook will rebuild it on next start.

Fix 4: Check File Permissions and Run as Administrator

Sometimes Windows updates or security software change permissions on your Outlook data folder. To test:

Right-click the Outlook shortcut and select Run as administrator. If the error goes away, permissions are the issue.
Permanently fix by right-clicking the shortcut, go to Properties > Compatibility, and check Run this program as an administrator.
Alternatively, navigate to your PST folder (e.g., C:\Users\YourName\Documents\Outlook Files), right-click the folder, select Properties > Security, and ensure your user account has Full control.

Fix 5: Disable Problematic Add-ins

Add-ins can interfere with Outlook’s mail operations. To test:

In Outlook, go to File > Options > Add-ins.
At the bottom, select COM Add-ins in the Manage dropdown and click Go.
Uncheck all add-ins, restart Outlook, and try again. If the error stops, re-enable them one by one to find the culprit.

Frequently Asked Questions

Why does error 0x80040600 happen only on one account?

Because each account has its own data file. The error is tied to the specific PST or OST file of that account. If only one account fails, focus on that account’s file (repair or reduce size).

Will I lose emails if I run ScanPST?

No, ScanPST repairs the file without deleting emails. However, it may move corrupted items to a folder called “Lost and Found” inside Outlook. Check that folder after repair and move items back if needed.

Can I increase the 20 GB PST limit?

No, the 20 GB limit is hard-coded in classic Outlook. Microsoft 365 subscriptions raise it to 100 GB, but for standalone Office 2016/2019, you must stay under 20 GB. The only workaround is to archive or use a different account type.

Does this error affect Outlook on other Windows versions?

Yes, error 0x80040600 can appear on Windows 7, 8, and 11 as well. The fixes are the same on all versions, but the ScanPST path may differ slightly.

What if none of these fixes work?

If the error persists, the PST file may be severely damaged. You can try creating a new Outlook profile (Control Panel > Mail > Show Profiles) and importing the old PST via File > Open & Export > Import/Export. If that fails, consider a third-party PST repair tool, but always test on a copy first.

General steps for current mainstream versions; menus can differ by device and version. See the disclaimer or report an error.

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