View, search, and export email messages without Microsoft Outlook, The easiest way to open PST and OST files without Outlook is to use OST PST Viewer. PST Walker Viewer (pstwalker.exe) can be used as a portable application or installed as a Windows application. PST Viewer protects valuable file metadata, you can safely open an Outlook data file without leaving a digital footprint.

Portable viewer for .pst and .ost files
PST Viewer is a good solution, when you need to view your mailbox: emails, contacts, tasks and attachments all together in one place.
Show the emails in its original format, whether it's HTML, RTF or plain text. Reply, or Forward items using your default email client
Support for various encoding settings to correctly display regional characters (such as ü, ä, ø, etc.) and Asian language characters
Open healthy, password-protected, and corrupted PST and OST files
Find items that were permanently deleted instead of moving to the Deleted Items folder in Outlook (hard deleted items)
Find items that are no longer associated with any folder in Outlook (orphaned items)
Command line options to open, recover and export emails from PST and OST files

Excel-like filtering, Instant search
Need to find an important message in a folder with your email files? Sort and filter your emails using the PST Viewer Excel-like filtering interface. Your settings for sorting and arranging items in a Folder View apply until you change them.
Review highlighted keywords so you don't need to look for the search criteria
Refine your search using the boolean search operators and functions
Highly efficient search algorithms, you spend less time waiting for results

Instant access to email headers and all message properties
Email is the most utilized form of communication for businesses and individuals nowadays, and it is often exposed to illegitimate uses. If you are a forensic investigator, you are probably need to be able to determine if an email has or has not been falsified.
The first steps in any investigation are to identify all the potential sources of information. Outlook data files (.pst and .ost) contain numerous metadata fields (MAPI properties) that can be useful for digital forensic analysis of emails.

What's New
official site does not provide any info about changes in this version