How do I manage duplicate contacts in Microsoft Outlook?

Q: How do I manage duplicate contacts in Microsoft Outlook?

A: If you use Outlook regularly, you’ll undoubtedly run into duplicate items from time to time. Typically, duplicate items result from actions taken outside of your normal day-to-day operations. The most common example is importing data (e.g., a .pst file). The biggest culprit in creating duplicate items is probably when you import contacts.

Outlook has a method for managing duplicate contacts during the import process. If you try to import a contact with an existing name or email address, Outlook will generate a duplicate contact error. Whether you’re importing contacts from a flat file (e.g., .csv file, Microsoft Excel spreadsheet) or from another source (e.g., .pst file, address book from another application), Outlook will provide you with the following three options:

  1. Replace existing item with the imported duplicate
  2. Allow Outlook to create duplicate entries
  3. Disallow the duplicate item to be imported

Figure 1 shows these options as they appear in Outlook. These options exist whether a user is importing contacts into the contacts folder, another folder in the mailbox, or a public Exchange Server folder (with permission of course).

When importing a large number of contacts where duplicates are likely to exist, you might want to clean up the content if possible before you import it into Outlook, so that you can select the first or third option with more confidence. The problem with allowing Outlook to create duplicates is that Outlook has no native mechanism for resolving duplicates after import. In addition, no “undo” feature exists after importing into Outlook. Removing duplicate contacts is a fairly manual process. One solution is to export existing contacts into the same format as the source to be imported, then compare those files. This approach works well with .csv files, using a tool such as csvdiff.

If you encounter a case in which every imported contact is a duplicate, such as if you import from the same source twice, as Figure 2 shows, Outlook has an optional view that lets you manually remove the duplicates. This view is based on a common property for each imported item—Modify date. In the Contacts folder with the duplicate entries, view the contacts by phone list by selecting View, Current View, Phone List. Then right-click any of the column headings and select Field Chooser from the context menu. Drag and drop the Modified heading to a place among the column headings. Finally, click the Modified heading to sort the entries by modified data and time. This action groups the imported content based on the date and time it was imported. You can then easily select and delete items from a specific time. Figure 3 shows this view with a duplicate contact selected.

Outlook can also prompt the user when adding individual contacts to a folder where a significantly similar contact already exists. This feature is optional; to enable it, select Tools, Options, Contact Options. Select the Check for duplicate contacts check box in the configuration dialog box, as Figure 4 shows.

When attempting to save a new contact that already exists, Outlook displays a resolution window, as Figure 5 shows. In this example, a new contact was created with the same name and email address, but with a different postal address. Outlook detects the duplicate and provides the user with the option to merge the new information into the existing contact (the radio button that is selected in Figure 5), add it as a separate contact, or cancel to prevent the addition.

I mentioned that removing duplicate contacts is a manual process—which is true if you limit yourself to Outlook’s native tools. Manually deleting contacts is reasonable if you need to delete a bulk import, but not if you have hundreds of duplicate contacts not bound by a common property. Situations such as this one might call for one of the many third-party applications that can solve such a problem. Sperry Software ( and MAPILabs ( both have effective duplicate remover add-ins for Outlook, for contacts and other Outlook items.

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