Fix CACHE_E_NOCACHE_UPDATED 0X80040170 Outlook Error

When You'll See This Error

You're working in Outlook 2016, 2019, or Microsoft 365 and suddenly you can't send or receive emails. The progress bar at the bottom says "Updating cache" and then stalls. After a minute, you get a pop-up: CACHE_E_NOCACHE_UPDATED (0X80040170). This usually happens after a network drop or if your computer went to sleep while Outlook was syncing.

What's Going On

Outlook stores a local copy of your mailbox in an OST (Offline Storage Table) file. This is what it syncs with the server. When that file gets corrupted—say a write operation was interrupted—Outlook can't update it. It's not a server issue. It's a local file that's borked. The real fix is to force Outlook to rebuild that file from scratch. You don't need to delete any emails. You don't need to call your IT department. You just need to tell Outlook to start fresh.

Step-by-Step Fix

Step 1: Close Outlook Completely

Don't just minimize it. Right-click the Outlook icon in the system tray (bottom-right, near the clock) and choose Exit. Wait 10 seconds. Open Task Manager (press Ctrl+Shift+Esc) and check the Processes tab. If you see any Outlook.exe or MSO.exe processes still running, right-click them and choose End Task.

Step 2: Rename the OST File

We're going to rename the current OST file so Outlook creates a new one. Open File Explorer and paste this path into the address bar:

%LOCALAPPDATA%\Microsoft\Outlook

This opens your Outlook data folder. You'll see a list of files. Look for a file that ends in .ost. It's usually named after your email address or mailbox name, like user@company.com.ost. Right-click it and choose Rename. Change the extension from .ost to .ost.old. So it becomes user@company.com.ost.old. Hit Enter.

Note: If you don't see file extensions, click the View tab in File Explorer and check the box for File name extensions.

Step 3: Restart Outlook

Open Outlook again. It will show a message like "Outlook couldn't find your local data file. We'll download it from the server." Click OK. Outlook will start creating a fresh OST file. This can take anywhere from 2 minutes to 20 minutes depending on the size of your mailbox and your internet speed. You'll see "Updating cache" in the status bar. Wait until it finishes. Don't close Outlook during this process.

Step 4: Test Send/Receive

Once the cache finishes updating, send yourself a test email. Sending to your own address works fine. If the email arrives in a few seconds, you're good. If you still get the error, move to the next section.

What to Check If It Still Fails

If renaming the OST didn't work, here are three things to check:

Are you in cached mode? Go to File > Account Settings > Account Settings. Select your email account and click Change. Under Offline Settings, make sure Use Cached Exchange Mode is checked. If it's not, check it and restart Outlook.
Is your mailbox too big? If your OST file was over 50 GB (common with Exchange Online), Outlook might struggle to sync. Archive old emails using the File > Tools > Mailbox Cleanup tool. Then repeat the rename process above.
Antivirus blocking? Some antivirus software locks OST files during scanning. Temporarily disable your antivirus for 10 minutes and try sending/receiving again. If it works, add an exception for the Outlook folder in your antivirus settings.

If none of these help, you might have a corrupt profile. Go to Control Panel > Mail > Show Profiles, create a new profile, and set it as default. That's the nuclear option, but it almost always kills the error.