While you can remove duplicates by hand, the tools on this page make it easier when there are a lot of duplicates. Although some of these tools work only with the mail folders, many will work on any Outlook folder that contains duplicates.

Manually Remove Duplicates

To remove duplicates, you need to use a single line table view, either by turning off the reading pane (View tab) or by dragging it to the right to make it narrower (on smaller screens, you may also need to collapse the navigation pane and To-do pane). In Outlook 2016, you may want to turn off Message Preview.

If you are using the the default group view in email folders, click on the field names above the message list and deselect Show in Groups.

For email folders, all standard views use a table view and you just need to turn off grouping and move (or turn off) the reading pane to enable the single line view. In the calendar, choose Events or By Category view, or in Outlook 2010 and up, the List view. Use Phone view or a list view in Contacts.

With a single line view:

1. Right-click any column heading, then choose Field Chooser.
2. In the Field Chooser, switch from the Frequently-used fields list to Date/Time fields, and then drag the Modified date field to the view to add it to the fields displayed.
   
3. Click on the Modified column header to sort by that field.
4. You should now see your Outlook items in reverse chronological order.
5. Click on the first item you want to delete.
6. Use the scroll bar to find the last item with the same modified date.
7. Hold down the Shift key as you click on the last one. This selects all the items between the two selections.
8. Press Delete to remove them all from the folder.
9. Reset the view when finished.

This method works well with imported items or when you re-download messages left on the email server because you'll have one set of items with the same modified date.

Deleted Duplicated Email Video Tutorial

The steps for Outlook 2003 and up are basically the same, except for the menu commands to turn the reading pane off and on. The first half of the video was recorded in Outlook 2010, the second half in Outlook 2007.

To turn the reading pane off and on in Outlook 2010, go to the View ribbon and expand the Reading pane menu.

Tools in the Spotlight

4Team Duplicate Killer	Outlook Duplicate Killer is an add-in for Microsoft Outlook. Find, merge and remove Outlook duplicates. Compare, assign the category, flag and move duplicates to selected folders. Find and remove duplicate contacts, emails, calendar events, tasks and notes automatically. Manage duplicates in any Microsoft Outlook folder, including Microsoft Exchange and Public folders. Preview duplicate search results prior to processing. New Duplicate Killer has improved user interface. Now account name and folder path are display.
Duplicate Email Remover	Finds and removes duplicates, even if the messages appear in different folders. Delete, move, or copy duplicates to any folder. Mark duplicate messages with a flag. Search for duplicates in the same folder, or in different ones. Process duplicates in Public folders on the Exchange Server.
ReliefJet Essentials for Outlook	ReliefJet Essentials is a set of 162 utilities for Outlook, Office 365 and Exchange Server. It can backup, import, export and convert data into different formats. Perform personalized mass mailings. Save, remove and optimize attachments. Find and remove duplicate messages, contacts, appointments, meetings, and other items. Retrieve statistics on email usage and get reports on Outlook data and settings. You can run the utilities directly from Outlook, automatically in rules, via standalone app, or from the command line.