Yes, you can merge unlimited PST files at once by using a professional utility like GainTools Merge PST Tool. This application lets you combine several Outlook PST files into one PST file without losing any data. There are no severe limits on how many files you can add to the software panel. It lets users choose multiple PST files at once and swiftly combine them while keeping all of the email's attributes, like attachments, contacts, calendars, and folder structure. The utility can read PST files made in different versions of Outlook and works with both ANSI and Unicode PST formats. You can just combine PST files into one file by adding them, choosing where to save the new file, and clicking the merge button.