If Outlook is filling up with duplicate emails, the easiest way to remove them is by using a dedicated duplicate remover tool. You can try manual methods like sorting emails by date/subject and deleting duplicates or using "Clean Up" in Outlook, but they don’t always catch everything.

For a reliable and automatic solution, the SysTools Outlook Duplicate Remover Tool works great. It scans your PST/OST files and removes duplicate emails, contacts, calendars, etc., without affecting original data.