While I was going through the problem in which I created the old PST files with older Outlook versions, needed a way to import all their data into larger single PST files that can be used with newer Outlook versions. Thus, in essence, I required to merge multiple PST files.
I gave a try to the manual method as Microsoft does not provide any tool for merging but, there's a built-in Import feature that you can use.
Though it doesn't merge PST files, you can import the mailbox content from two or multiple PST files into a single file so like creating a blank PST and then merging the PST file into a newly created blank PST by following some steps, it worked.
You just to need to follow these simple steps:
1: First, launch Microsoft Outlook on your system.
2: Create a new Outlook data file. Click New Items, point to More Items, and click Outlook Data File...
3: On the Create or Open Outlook Data File window, give a name to this new file. Click OK to confirm your action. You can see the new Outlook data file in the navigation pane.
4. On the taskbar, click File tab > Open > Import.
5. On the Import and Export Wizard, select Import from another program or file in the option. Click Next to continue the process.
6. On the Import a File window, select Outlook Data File (.pst). Then click Next.
7. On the Import Outlook Data File window, click Browse to locate the file and select it. You can see the selected file in the edit box. You may check the box Do not import duplicates box, and then click Next.
8. Now select the folder to import from. You may check the box Include subfolders. Keep it unchecked if you don't want to include subfolders in the output PST file.
Also, check either Import items into the current folder or Import items into the same folder. Finally, click Finish.
Step 9. Outlook starts importing the selected mailbox folder to a new PST file.
P.S: For merging a large number of PST files, this manual trick turns into a time-consuming process. Also, keep in mind that you can't use the above trick if the PST files are corrupted.
Users who are not familiar with Outlook wizards or other technical terms may find these steps slightly difficult.
So the Professional method can be considered widely in this process as it's not tricky and user friendly, I would recommend you to go for my personal favorite PST merge tool is Stellar Merge Mailbox for Outloo
k. I have used this tool many times and I think it makes your PST easy to handle. Although merging PST can be attained manually, but it's easily prone to corruption and the process does not guarantee success. But doing it with a tool is safe and hassle-free for satisfactory results.