Puzzling Outlook Bug: Non-Stop Prompts for OST/PST-File Repair

I’ve been working with Outlook since the mid-2000s, so I’ve seen plenty of crazy things. However, I was recently stumped by a PST-file repair prompt issue I’d never seen before. Anyone who knows Outlook is very familiar with the ScanPST utility and the reality that OST/PST files can become corrupted under the right conditions: imminent drive failure, when the PST file is too large, or if changes to the PST file were incomplete.

Bad Outlook Hygiene is Rampant

My worst offender was a customer with a 50 GB PST file, who simply refused to delete any email and who would regularly manually move huge folders of mail into separate PST files. They also had a propensity to force-close Outlook any time it was running slowly. Combine these bad habits with slow 5400RPM hard drives and the CPUs of yesteryear and the result was monthly or weekly PST file corruption, and a lot of time spent repairing PST files.

…But Bad Outlook Hygiene Wasn’t the Cause This Time

About a week ago I was surprised when I received the prompt to repair my own PST file. I always figured I was immune to this issue, since I keep my data file sizes low, everything I own is Solid State, and I keep my Outlook configuration simple. I ran the repair, and restarted Outlook, and received the same prompt again. I ran the repair again, on the same PST, and still the prompt showed up when I opened Outlook!

As far as Outlook troubleshooting goes, the next step is always to open Outlook in Safe-Mode. Maybe something is stuck? Still the same prompt. I checked for Office updates by pulling up Microsoft Word, but there were no updates. The next logical step is to create a new Outlook profile, but that didn’t work either. Still the same prompt—even though the new profile should be using a different PST!

At this point, I knew something wasn’t right. Time to nuke it from orbit. I completely uninstalled all Office 365 apps, rebooted, then reinstalled. Launched Outlook and my jaw dropped when I received the same exact prompt again! I navigated to the directory mentioned in the prompt and it was empty! No OST or PST files in sight! How frustrating!

Check Registry Editor

It was at this point I decided to start checking online. Researching any Outlook issue online can be hit or miss due to the extremely high volume of information regarding similar issues. But after about ten minutes, I was able to find something interesting—a single registry key enables or disables the PST Prompt for Repair. When enabled, the prompt will show EVERY time.

Computer\HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Outlook\PST\PromptRepair

I opened my registry editor and found the key. Sure enough, it was enabled! Setting the key to 0 disabled the setting and immediately Outlook was fine and opened right up. Such a simple fix yet creating a new mail profile and reinstalling Office from scratch didn’t take care of it! Sounds like Microsoft may need to make sure that registry key setting is disabled when Outlook is uninstalled or when a new mail profile is created.

Is an Office update to blame? I suppose we may never know, but I’m going to keep watching for this issue to come up again. Regardless, I hope this information is helpful to someone out there and saves you the time of reinstalling Office.