ANSI PST files do not work on new versions because they are old PST files that have been made smaller, while Unicode PST files work on all new versions, such as Microsoft Outlook 2021, 2019, 2013, 2007, etc., and also work on Windows OS 11, Windows 10, Windows 8, and Vista. You can use the OSTTOPSTAPP ANSI to Unicode converter to convert ANSI PST files. Unicode PST files are created with unlimited file sizes. Transforming your ANSI PST file to a Unicode PST will allow you to take benefit of newer Outlook features, including larger storage capacity, improved performance, and support for multilingual data.