There was a download of Outlook PST Merger 3.0 on the developer's website when we last checked. We cannot confirm if there is a free download of this software available. We recommend checking the downloaded files with any free antivirus. This program was originally created by MailConverterTools. The most popular version of the tool is 3.0. The program lies within System Utilities, more precisely HDD Management.
From the developer:
The PST Merger tool is specialized in executing the merging process within seconds. The software is able to merge the PST data in different methods such as Merge PST, Join PST & Merge Contacts. The PST Merger software will efficiently eliminate all the carbon-copy of the PST items. The software is able to eliminate or remove the deleted items from the merging process. The Merge Outlook software provides the password to the newly merged PST files.
You may want to check out more software, such as DataVare Outlook PST Merge Exprert, KDETools PST Merge or KDETools Outlook PST Recovery, which might be similar to Outlook PST Merger.
General