Microsoft Outlook is a popular email client application that provides a wide range of features to its users. It is not just an email client. It in fact works as a personal information manager that not only stores your crucial mailbox data, but also manages them in an accurate manner. It creates an Outlook data file aka PST or personal storage table for storing all the mailbox data of a particular email account which is configured with the Outlook email client. Outlook provides an option for configuring multiple email accounts at a time.

Being an Outlook user, you must have seen duplicate items in your Outlook PST files. There could be many reasons for having duplicate items, such as: email messages, contacts, calendars, tasks, notes, journals, etc. in Outlook. For example: you are receiving multiple copies of the same email message many times from any of your friend or a teammate. This is the most probable reason for having a large amount of duplicate items. There could be some other reasons as well, but they are not so obvious.

• If you perform an incorrect synchronization with the laptop or mobile device or the synchronization process gets interrupted by any reason, chances for having duplicate items may increase.
• Duplicate emails can also be produced by a fault in mail server, especially when you activate the “Leave Messages on the Server” settings option.
• If the Outlook rules have been configured incorrectly, i.e. if two or more “move a copy to” rules are applied to a certain incoming message, it may also lead to email duplication.
• Sometimes merging multiple PST files into a single file may cause duplication in email messages or in other mailbox items.
• An antivirus software may also create duplicate items in your Outlook PST files.

Having multiple copies of the same messages or other email items may cause confusion or disorder in your MS Outlook email client. If your PST file contains a wide range of mailbox data, your Outlook will consume more memory, disk space and CPU usage. And after a while, your Outlook will start to slow down in performance. Usually Outlook starts to slow down when the size of mailbox reaches 2 GB or exceeds this size limitation.

How to delete or remove duplicate items from Outlook PST files?

There are two ways by using which you can delete or remove duplicate items from Outlook PST files. You can either try a manual trick or you can employ a third-party utility. Though the manual trick may take some time, but it is very simple and easy-to-perform.

If you want to try the manual trick first, you need to follow the steps given below:

For MS Outlook 2007 or any earlier version

• Launch Microsoft Outlook on your system, and select the folder from which you want to delete the duplicate items.
• If you are using 2007 or 2002, click on the View tab and point to Current View. Or if you are using 2003, click on the View tab and point to Arrange By.
• Now change the folder view to a table type view.
• You can use the following combinations of views and fields:

View: Calendar, Contacts, Inbox, Journal and Notes

Field: Active appointments, Phone list, Messages, Entry list and Notes list.

• You need to right-click on column heading and then click Field Chooser from the options.
• Now select a field from the list which is shown at the top of Field Chooser. For e.g. you can select All <item name> fields by clicking it.
• You need to drag down the Modified field to the table heading.
• Make sure the duplicate items you want to remove have a unique date from the original set of items. Click the Modified heading in order to sort the items by this field.
• You need to select the items which you want to remove. You can select all the items by clicking the first item and then the last item by holding down the Shift key.
• Now press Delete to permanently delete all the selected items.

For MS Outlook 2010

• Launch Microsoft Outlook on your system, and select and folder from which you want to delete the duplicate items.
• Click the View tab of the ribbon and then click Change View.
• Now change the folder view to a table type view. For e.g. click the List icon.
• You need to right-click on column heading and then click Field Chooser from the options.
• Now select a field from the list which is shown at the top of Field Chooser. For e.g. you can select All <item name> fields by clicking it.
• You need to drag down the Modified field to the table heading.
• Make sure the duplicate items you want to remove have a unique date from the original set of items. Click the Modified heading in order to sort the items by this field.
• You need to select the items which you want to remove. You can select all the items by clicking the first item and then the last item by holding down the Shift key.
• Now press Delete to permanently delete all the selected items.