There are many tools for removing duplicates in Outlook, and the Regain Outlook Duplicate RemoverTool is one of the best and the most reliable ones. The software is so built to remove duplicate items from emails, contacts, calendars, and tasks of Outlook PST, OST, and BAK files. It also supports all versions of Outlook, such as Outlook 2021, 2019, 2016, and Outlook 365. Its intuitive user interface allows you to easily identify and delete duplicates from multiple PST files. There is an available free trial version, and for more info, check out Regain's official website.