A simple way to remove duplicate from Outlook is to first back up your PST file and then check for duplicates manually by sorting your emails. While this works for smaller inboxes, it becomes difficult if duplicates are spread across multiple folders.

For a quicker solution, tools such as SysInfo Outlook Duplicate Remover can automatically scan your mailbox and identify repeated emails. After the scan, you can choose whether to delete duplicates permanently, move them to another folder, or create a new PST file without duplicate items. This approach saves time and keeps your mailbox organized.
Read more: https://www.sysinfotools.com/recovery/outlook-duplicate-remover.php