ODIR is a free Windows utility that integrates itself with Outlook. Once installed, it clean your Outlook folders by removing all duplicates. ODIR removes duplicates from Contacts; Calendar; Tasks; Notes and Email folders.
Using ODIR is very easy: select a folder and click the button Remove Duplicate Items. ODIR scans the selected folder for duplicates and MOVES all duplicates found to a subfolder ODIR_duplicate items. ODIR recognizes an item as a duplicate if all of the following properties match those of another item in the same folder: