Advanced data recovery of inaccessible or corrupt Outlook .PST and .OLM files


Advanced data recovery of inaccessible or corrupt Outlook .PST and .OLM files Data Recovery Ireland


Outlook is a popular email application for Windows and Apple platforms. For most users, it is more than just an email client as it performs as a calendar, contact manager and task organiser. It uses a message store file called .PST (personal store folder) as it’s native file format. We have been helping a number of our clients recently recover data from corrupt .PST files and recover .PST files from mechanically damaged hard disks. For some of these clients, their priority was the recovery of their emails. For others, it was their email, contacts and calendar.

Common Microsoft Outlook error messages

When Outlook opens with an error message about an inaccesible .PST it can be quite scary for the user and sometimes for the IT admin (who has no backup…). Common Outlook error messages in Windows include:


Cannot open your default e-mail folders. The information store could not be opened.
Cannot start Micorsoft Outlook. Cannot open the Outlook window. The set of folders cannot be opened. The operation failed.
The file C:\Users\USERNAME\AppData\Local\Microsoft\Outlook\Outlook.pst cannot be found.
Cannot start Microsoft Outlook. Cannot open the Outlook window. The set of folders cannot be opened. File access is denied. You do not have permission to access the file C:\Users\USERNAME\Documents\Outlook Files\Username.pst

Some of these error messages are indicative that your .PST file has gone corrupt.

To understand how to recover .PST files, it can be helpful to know about the file’s architecture and format. In all versions of Outlook pre-2003, all .PST files were in ANSI (American National Standards Institute) format. From 2003 onwards, all .PST files are now in Unicode format which allows for 64-bit block IDs and absolute file off-sets. Typically, a .PST file is constituted of three layers. These include the Messaging Layer, the LTP layer (lists, tables and properties) and the NDB (Node Database) layer.

The structure of .PST files

Advanced data recovery of inaccessible or corrupt Outlook .PST and .OLM files Data Recovery Ireland

The messaging layer contains the message store, folder structure, messages and attachments. The NDB layer contains the lowest-level information about the .PST file such as header file and metadata pages. The LTP ( Lists, Tables and Properties) layer collects file properties. Because of the .PST’s proprietory status, Microsoft have not disclosed the algorithmic functions which are used to maintain integrity between the layers (the lousers…).

Data recovery or repair of .PST files

There are many “PST recovery tools” available to buy on the internet. Most of these promise the beleaguered user in search of a quick fix a “one click solution”. Sometimes they do work. But most of these utilities cannot handle extensive LTP, NDB or messaging layer corruption. The SCANPST utility can sometimes be successful if there just low-level corruption. However, if the damage if more extensive Drive Rescue can help with a complete data recovery of your Outlook .PST file.

The .OLM connection (Outlook for Mac)

The relationship between Outlook for Windows and Outlook for Mac is rather tenous. In fact, in Microsoftland the developement teams for both aplications are not in the same building or even part of the same business unit. As a result, while on the surface they do share similarities, their underlying architecture of both applications is quite different. The common Outlook for Mac 2011 application has a measly upper size limit of only 2GB. When your .OLM file goes corrupt you can try rebuilding the file by using the Microsoft Database Utility or by rebuilding your identity. If all this fails, professional data recovery for your .OLM file might be needed.

How to mitigate against data loss with Outlook

Use IMAP instead of POP3 – If you’re using Outlook 2007, 2010, 2013 or 2016 try to use IMAP instead of the POP3 protocol for your email configuration.(POP3 was not really designed for era of mobile email use). Because IMAP syncs your .PST with your mail server, should something go wrong with it, – you should be able to access a copy of your emails on your mail server.

Don’t let your .PST file get too large. Outlook 2003 and 2007 has a theoretical file size limit of 20GB. From our experience, however, for these versions of Outlook, once you let a .PST go above 16 to 17 GB in size, Outlook can start to go awry and you run the risk of your.PST file imploding. For Outlook 2010 and 2013 the .PST file size limit is a very generous 50GB.

Use Microsoft’s PST Back-up Tool – This handy utility from Microsoft allows you to backup your .PST by using an Outlook plug-in. In turn, you can use its output .PST file for on-line or local backups. This can be extremely useful because when you have Outlook open, a substantial number of backup applications still refuse to back-up a .PST because it is a “file already in use”. Having a second up-to-date .PST file for back-up purposes is a great workaround to this common problem.

Use Outlook Office 365 – With this option your .PST is stored in the Cloud. This can mitigate the risk of data loss due to disk failure but does not protect against events like file corruption. For this, it is recommended that you use an Office 365 solution such as Cloudally or Backupify.

In the event that you or one of your users has lost access to their email store file, Drive Rescue offers an advanced .PST and .OLM data recovery service for corrupt files or files that are inaccessible due to disk electronic or mechanical faults. Call us on 1890 571 571.