Voimakas PST Merge is described as 'Tool to easily merge more than two or multiple PST files into simple one PST file including all email items. It is one of the best software to merge PST files successfully'. There are three alternatives to Voimakas PST Merge for Windows, Microsoft Exchange Server, Microsoft Office 365 and Microsoft Office Outlook. The best alternative is Merge Folders for Outlook, which is free. Other great apps like Voimakas PST Merge are SysTools PST Merge (Paid) and SysInfo PST Merge (Paid, Open Source).
This free tool merges multiple Outlook folders: select one or more source folders, specify the destination folder, and run the utility. You can save the subfolder structure, move data from source folders, ignore duplicates and specify date range.