To merge multiple PST files into single PST file, you can use KDETools Merge PST files software. It provides a safe and easy option to merge PST files. Have feature to removes duplicate items and excludes deleted items in the merging process. This utility merges various MS outlook contacts, outlook emails, and outlook calendars into one PST file with great ease.
PST Merge Tool combines Outlook PST file in the most effective way possible. This application is very advanced software to merge PST files. This software takes almost no time to finish merging multiple files. Users do not have to worry about the file size as this tool merges files regardless of their size. It does not make any changes in the data saved in the PST file. Also, it can merge data of PST files and folders. PST Merge Tool is compatible with all the versions of Windows OS and MS Outlook. You can also download the demo version of this software from here:-https://www.betavare.com/merge-pst/