Outlook (classic) · Windows

Outlook Data File Cannot Be Accessed (0x8004010f)

The error "Outlook data file cannot be accessed – 0x8004010f" usually points to a corrupt Outlook profile or a damaged offline data file (.ost), often when Outlook tries to send, receive or download the Address Book. For IMAP and Microsoft 365 accounts the fix is safe and easy: let Outlook rebuild the .ost, or build a fresh profile, from the server. Nothing is lost because your mail lives online. Rated 4.9 on Google.

Fix this error remotely See how remote support works

● Classic Outlook
● IMAP / Microsoft 365
● Safe .ost rebuild

Why it happens

What error 0x8004010f means

Error 0x8004010f most often appears during Send/Receive with the message that the Outlook data file cannot be accessed. Microsoft's own guidance puts this down to a corrupt Outlook profile. For a modern IMAP or Microsoft 365 account, Outlook also keeps a local offline copy (.ost) of your mailbox, and a damaged .ost can trigger the same error. Sometimes it's simply that Outlook can't download the Offline Address Book.

The reassuring part: with IMAP and Microsoft 365 your real mailbox lives on Microsoft's servers. The .ost is just a local cache, so it can be rebuilt with nothing lost — Outlook re-downloads everything. (This is different from a POP .pst, which is your only copy — if you're on POP, don't delete anything; see our PST cannot be accessed guide instead.)

// NEED THIS FIXED RIGHT NOW?

Skip the DIY — call 01202 775566 and we can be looking at your screen within minutes. You watch everything we do, and most problems on this page are fixed in one short remote session. (Mon–Fri, 9am–5pm.)

Start SOS Remote Support Call 01202 775566

The fix

How to fix "Outlook data file cannot be accessed"

Try these in order — for IMAP and Microsoft 365 they're all safe, because your mail is held on the server:

Download the Address Book. If the error only appears when sending, go to Send / Receive > Send/Receive Groups > Download Address Book, untick "Download changes since last Send/Receive", pick your Global Address List and click OK. Sometimes that's all it needs.
Rebuild the offline file (IMAP / Microsoft 365 only). Fully close Outlook. Open File Explorer, paste %localappdata%\Microsoft\Outlook into the address bar and press Enter. Find the .ost file for your account and rename it (for example add .old to the end) rather than deleting it outright. Reopen Outlook — it builds a fresh .ost and re-downloads your mail from the server. Nothing is lost.
Check which profile and account Outlook is using. Go to File > Account Settings > Account Settings and make sure your main account is present and listed as the default (highlighted) on the Email tab. Note: for an IMAP or Microsoft 365 account you can't manually "Set as Default" the .ost on the Data Files tab — Outlook manages that automatically, so if that button is greyed out, that's normal and not the fault. If the wrong account is default, the reliable fix is a fresh profile (next step).
Create a fresh mail profile. This is Microsoft's documented fix for 0x8004010f. Close Outlook, open Control Panel > Mail (Microsoft Outlook) > Show Profiles > Add, create a new profile, add your account, then set Outlook to always use it. On IMAP/Microsoft 365 your mail simply re-downloads from the server.

As long as you're on IMAP or Microsoft 365, every step here is safe — your email is held on the server and comes straight back.

FAMILY-RUN SINCE 1995 · ★ 4.9 ON GOOGLE · 200+ COMPUTERS UNDER OUR CARE · NO FIX, NO FEE · SAME-DAY REMOTE SUPPORT

// GOOD QUESTIONS

Frequently asked

What does "Outlook data file cannot be accessed 0x8004010f" mean?

Microsoft attributes it to a corrupt Outlook profile; a damaged offline data file (.ost) or a failure to download the Offline Address Book can also cause it. On IMAP and Microsoft 365 accounts the fix is to rebuild the .ost or the profile from the server, which loses nothing.

Is it safe to delete the .ost file?

On IMAP and Microsoft 365 accounts, yes — the .ost is only a local cache of a mailbox that lives on the server, so Outlook rebuilds it and re-downloads everything. To be extra safe, rename it (add .old) rather than deleting, so you can restore it if needed. Never delete a POP .pst this way, as that is your only copy.

Where is the .ost file stored?

In %localappdata%\Microsoft\Outlook. Close Outlook first, paste that path into File Explorer's address bar, find your account's .ost, and rename it — Outlook creates a fresh one and re-syncs on the next start.

Why can't I "Set as Default" my .ost data file?

For IMAP, Microsoft 365 and Exchange accounts the Set as Default button on the Data Files tab is greyed out by design — Outlook manages the default automatically, because those accounts keep calendar and contacts on the server. That's normal. If the wrong account is set as default, create a new mail profile instead.

What's the difference between 0x8004010f and 0x80040116?

0x8004010f typically points to a corrupt profile or offline .ost (IMAP/Microsoft 365) or a missing Address Book, and is safe to rebuild from the server. 0x80040116 points to the main .pst data file being missing, locked or corrupt — see our separate PST cannot be accessed guide for that one.

Can you fix the 0x8004010f error for me remotely?

Yes. We connect via secure remote support (you watch throughout and we phone you first), rebuild your offline file or profile cleanly from the server and confirm your email is flowing again — usually within minutes. Call 01202 775566.

Send/Receive keeps failing?

We'll connect remotely, rebuild your offline file cleanly from the server or build a fresh mail profile, and confirm your email is flowing again — usually within minutes. You watch the whole time, we phone first, and access ends the moment we're done.

Fix this error remotely See how remote support works

01202 775566 · help@365techies.co.uk · MON–FRI 9AM–5PM