You can combine Inbox folders from multiple Outlook PST files into a single folder in a variety of ways. But don't worry, I only got the thing for you. I decided to do the same with the inbox folders in my Outlook PST file. However, I could not remember important details. Then I went to Google and found a lot of amazing apps. I also recommend ToolsBaer Outlook PST Merge Software. It can integrate Outlook email, calendar, contacts, and notes, among other features. It was fully compatible with all versions of MS Outlook and Windows OS. The program can combine multiple PST files into a single PST without modifying the original. Outlook PST Merge works with all versions of Microsoft Outlook. It is compatible with Windows 10, 8.1, 8, 7, XP, and Vista, as well as all versions of MS Outlook until 2021. The service is accessible for free as a trial version.