How To Merge Multiple PST Files
If you need to merge multiple Outlook PST files, then you can try the best PST Merger tool. This tool helps to merge multiple PST files into a single PST file. It can merge PST files in both ANSI and UNICODE formats. The software allows you to join PST, combine PST, or merge PST and its data items such as contacts, calendar, notes, journals, and so on into a new single PST file while preserving data integrity and preventing data loss.

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Diana Carvalho commented
Managing the multiple Outlook PSTs is a bit daunting task. Handling more than one PST file seems a minor problem at the initial level, but it isn't easy to cope with in the long run. If you are one of those who are thinking of getting rid of this problem, then you need to merge PST files using the available solution. We recommend users try Shoviv PST Merge software to merge multiple large-size PST files into a single PST File.
Read more - https://www.shoviv.com/blog/how-to-merge-pst-files-manually/