I found myself having to use the repair tool after installing last week’s KB3097877 update. This was a security update issued for Windows that had the side effect of making Outlook crash when viewing certain HTML-formatted email messages. After several crashes, I noticed a small cog icon had appeared in on the status bar at the bottom of the screen. This meant that Outlook had found its data files to be corrupted and was attempting repair in the background.
My main Outlook data file is around 23 gigabytes, and so any background recovery would take a long, long time. Instead, I made use of the Microsoft Outlook Inbox Repair Tool, also known as ‘scanpst’, which is designed to repair errors in Outlook’s PST and OST files.
The program is installed at the same time as Microsoft Office, and usually sits in the same folder as your office programs. On my computer, this was C:\Program Files\Microsoft Office\Office14 (as I’m using Office 2010). It’s a simple program – you open it, point it at your Outlook data file and let it scan. It’ll then tell you whether a repair is necessary, and, if so, it’ll start the recovery process.
I would suggest finding other things to do whilst the tool runs, because the recovery process can take a very long time – especially on big data files like mine. In my case, it took over two and a half hours for the repair phase, having taken almost an hour on the initial scan for errors. During this time, you can’t use Outlook, as the data file is in use by the recovery tool.
Once the tool has finished, you can then re-open Outlook, and hopefully any missing emails will re-appear. It’s not guaranteed though, which is why it’s best to use a server-based email system like IMAP or Microsoft Exchange, rather than POP3 where emails are downloaded to your computer and then deleted from the server. That being said, Microsoft advises against repairing OST files, used for online accounts. Instead, it suggests that you simply delete and re-add the account in Outlook, to re-download a fresh copy of the data from the server.