One of the best and top-notch solution for removing the duplicate PST files is
Aryson Outlook PST Duplicate Remover. It is an efficient solution which easily detects and remove the duplicate PST files in a few minutes to increase the storage space. Additionally, the software allows you to see the Preview of PST files details such as sender, total message count, subject, attachments, dates, and email messages and also offers a Date Range feature to remove duplicate emails within a specific date & time. There se free demo version which allows you to remove up to 50 items from PST folders for free.