I have been working with an Outlook PST file that has accumulated emails over several years, and recently I noticed that many messages appear more than once. The duplicates seem to have been created after importing older mail and synchronizing the account multiple times. Some folders contain only a few repeated messages, while others have hundreds.

I do not want to delete messages manually because it would be difficult to determine which copy should be retained. Some emails have attachments, while others contain different metadata even though the subject and sender look identical. Is there a reliable Outlook duplicate remover that can identify duplicate items without affecting the original mailbox structure?

I am also concerned about other Outlook data besides email. The PST contains contacts, calendar entries, and tasks, and I would like to check whether duplicates exist there as well. Ideally, the software should allow me to review the detected items before permanently removing anything.

While researching different options, I came across the SysInfo Outlook Duplicate Remover. It is designed to find and remove duplicate Outlook items from PST files and supports duplicate removal for emails, contacts, calendars, and tasks. It also provides options for selecting folders and managing multiple PST files. This seems useful for cleaning up an older archive without manually checking every folder.

Another thing I would like to understand is how duplicate detection works. For example, if two messages have the same subject but different attachments or timestamps, I would not necessarily consider them duplicates. I would prefer a tool that compares relevant email properties before marking an item for deletion.

Has anyone here used an Outlook duplicate items remover on a large PST? What criteria did you use to identify duplicates, and did you create a backup before starting the cleanup? I would appreciate recommendations for handling duplicates safely while preserving the original Outlook data.