How to Steps
Removing Redundant Messages with Outlook Conversation Clean-up
1. On the Home tab, in the Delete group, click Clean Up.
2. Click one of the following:
Clean Up Conversation The current Conversation is reviewed, and redundant messages are deleted.
Clean Up Folder All Conversations in the selected folder are reviewed, and redundant messages are deleted.
Clean Up Folder & Subfolders All Conversations in the selected folder and any folder that it contains are reviewed, and redundant messages are deleted.