Outlook OST file cannot be opened with Outlook

It’s been just about a week since I set up Outlook with my corporate account and I got an error message when I opened another folder in Outlook after the system was restored from hibernation: The OST file cannot be opened. This wasn’t the first time this had happened to me, but none of the suggested solutions had helped me before. But now I’ve gained a bit more insight into how Outlooks work – which still isn’t enough to call me an expert or even knowledgeable on the subject, I’m just confident about the solution to share it. That’s the reason for the somewhat casual tone of the document.

So what did I do?

If this happens and you search online for this problem, most websites will state that this error occurs because the named OST file is corrupt. One of the solutions is to run the SCANPST.EXE tool that comes with your Office installation. This tool attempts to repair your OST file and reports that it was successful, but it did not fix the problem.

Another solution is to simply delete the file and have Outlook recreate it. The strange thing is that Outlook immediately complains that it cannot open the file, even though it contains no data. It creates a 0-byte file and still classifies it as corrupt. At this point I even consider reinstalling a tool, which I now realise would have been a much bigger waste of time.

I found this solution myself, but it sheds some light on the nature of the problem: Office comes with a mail setup tool that is also added to the control panel, and there you can change your data files, which are the default files, or even set up a cache for the service you are using. You can open the properties of a store, and in this window there should be a checkbox labelled ‘Use Cached Exchange Mode’. If you uncheck this, your emails will only be available when you are online, but at least you can now start Outlook.

After reassuring myself that I can finally use Outook again, I found an article about the same problem, which also mentioned the same setting I just found. But this article explains that this file saves all emails so that you can read them offline. It also explains that a sudden crash or shutdown can corrupt the file.

This got me thinking: Outlook is a huge system, and it’s not unlikely that it tracks the use of a file outside the system, so it’s possible that I can do what I want with the file while Outlook sees it as locked and can’t access it because a precondition isn’t met. So if I restart my PC, the problem should be fixed, right? and this article shows a different error message suggesting the same thing, while the article itself suggests restarting the entire Outook utility and services by hand.

Conclusion

So I restarted it. And now it works. Would this have been a solution from the start? I don’t know, but it’s entirely possible. My recommendation is: Whenever you are done for the day and want to shut down, hibernate or sleep your PC, quit Outlook first. If you haven’t followed this and have the same problem, restart your PC. I am surprised that this is not the first solution.