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Delete Duplicate Emails in Office 365 - Remove Items' Replication


In this blog, we will be discussing various issues where users face problems with email replication, why the users should delete duplicate emails in Office 365 and the methods to remove the emails using manual approach.

Recommended: Backup Office 365 mailbox to PST before deleting duplicate O365 items


Office 365 is a cloud-based application suite that is provided by Microsoft. There are millions of users who use it. MS O365 provides tools & services that help the users to access their documents, emails or collaborate from anywhere in the world. The subscribers of Office 365 suite get many user-friendly as well as business friendly tools that help in team building and business collaboration. The most commonly used application in Office 365 suite is OWA (Outlook Web Access). OWA is a web based service which is primarily used for sending & receiving emails.

Office 365 mailbox can also be accessed through the platform-dependent application which is Outlook, that can be accessed in MAC, Window, iOS. The most frequent issues faced by OWA/Outlook users is that they keep receiving duplicate or even triplicate emails, also their contacts & calendar entries get replicated. There are various forums flooded with such user queries. Let us discuss in detail about the problems faced by the users due to this Office 365 email replication.


"Outlook 2019 has updated its features today and since then I have been receiving same emails multiple times. I keep getting the same message 2-3 times. I am using a POP3 account and there are no duplicate or triplicate emails when I am using the web-mail. This email replication has just started today. I received an update message when I launched Outlook, so I am pretty sure that this error is happening because of the update. I ran ScanPST but there is no error in the data file. How can I delete duplicate emails from Office 365 Outlook 2016? What could be the reason for such bug?"

"Recenlty, I have uploaded my Outlook data. However, with it a lot of duplicate emails, contacts and calendars got uploaded. How can I remove these replica files? Is there any automated solution or an add-on remover function?"

"I am having thousands of Office 365 emails among which 200-250 emails are duplicate mails. Please help me with how to remove duplicate emails in Office 365. I am using Outlook 2016 for Windows."


The user mailbox of Microsoft Office 365 contains emails, calendars, contacts, etc. Just like other mailbox provider, O365 also provides maximum default storage capacity. If the limit is exceeded the users might face issues with accessing emails or various other performance issues. If the user has duplicate/ triplicate items in his mailbox, this may result in huge utilization of space on O365 cloud. So to avoid such scenarios, we should delete unnecessary or duplicate items from the mailbox. The presence of replica may result in slow performance or may even lead to mailbox corruption. Corrupt mailbox may lose your data and land you in a huge trouble. It is highly recommended to delete duplicate contacts, emails, & calendars in Office 365.

Let us now discuss how to delete duplicate emails in Office 365.


There is no direct automated procedure to delete duplicate emails in Office 365. Same is the case with duplicate calendars and contacts. The user will have to follow the manual approach as follows.

Manual approach to delete duplicate emails in Office 365

Delete each unnecessary items manually by selecting the files and then deleting them one by one.

-Limitation of Manual Method:

This manual approach is not recommended for the user as this procedure is time-consuming as well as inconvenient. The alternative approach to remove duplicate items from Office 365 is as follows.

Another manual approach is to use the PowerShell command



cmdlet in Exchange Online PowerShell. However, this method to remove items can be quite risky due to lack of granual control over deleted data.

Convenient Approach to Remove Replication in Office 365 Mailbox

We should extract the Office 365 mailbox containing emails, calendars, contacts, etc. to file with the help of a third party tool named, Office 365 Backup Tool. Launch the automated tool and login to Office 365 account, choose the items that you want to download to the file. Load the file in MS Outlook.

Now, follow the steps given below:

1. Delete Duplicate Emails in Office 365

  • Start MS Outlook and choose the files folder from which you want to remove duplicate items.
  • Go to VIEW Tab → Change View → Table Type View.
  • Click on Field Chooser by right-clicking on a column heading.
  • Select All <item_name> fields at the top of Field Chooser.
  • Drag the Changed field to table heading.
  • Check that the duplicate items have unique date from the original one. Sort the items by clicking the modified heading.
  • Choose the all the emails that you want to delete.
  • Click on DELETE option to delete the selected emails permanently.

2. Remove Duplicate Contacts in Office 365

Delete the duplicate contacts from Outlook desktop-based email client:

  • Choose the Contacts folder that contains duplicate contacts.
  • Go to current View Group → VIEW Tab → Change View → Click Phone.
  • Each contact will be listed on the to order of the phone numbers.
  • Select the contact with same phone number/email address and right-click on it to delete.

Recommended: To remove duplicate contacts in Office 365, the user can login to the OWA (Outlook Web Access) and then go to People → Contacts → Choose & Delete each replica contact manually.

3. Remove Duplicate Calendar Entries in Office 365

If you took a manual route to import Google calendar to Office 365 Account then following steps may help out to clear the clutter.

  • In MS Outlook, in the navigation panel go to Calendar → select the Calendar folder.
  • Go to current View Group → VIEW Tab → Change View → Click List.
  • Click the Subject column heading, to arrange the calendar entries by subject.
  • Choose all the duplicate calendar entries in the list that you wish to delete and click on DELETE.


Well, the above methods are a nice approach to remove duplicates items from Office 365. But in the manual method you have to delete duplicates from all items one-by-one from emails, then contacts, and then calendars. And all these steps make this procedure very long-winded.

Thus, to make the task easy for you here in this blog we are going to introduce the best-automated tool that can easily delete duplicates from Office 365 accounts. Outlook Duplicate Items Remover tool is well capable to remove duplicates from PST, OST, and BAK files. This is all in one duplicate remover utility that will delete all duplicate items from Office 365 emails, contacts, and calendars. In fact, the tool comes with various filter options such as Date Filter, Categories Filter, and Delete Action Filter

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Note: To use this tool first you have to configure your Office 365 account to the Outlook email client. Then you can easily add the OST file to the software for the duplicate removal process.


The duplicate removal facility is only part of premium OneDrive accounts. Moreover unlike Outlook where you can remove duplicate emails office 365 via PowerShell no such option is available on OneDrive. So free users will not find it. If you still want to remove duplicates you can use a workaround like this.

  • Make a new folder and name it Duplicate Detector.
  • Select all files in every subfolder and move them here.
  • Now manually scan through the folder and delete the ones that have a number at their end.

This method works because a single parent folder in OneDrive cannot contain duplicate files. That is why OneDrive automatically renames any duplicates by adding in a number with curved parenthesis. The number always starts with 1. However, be careful if you have used numbers in your naming convention; this might confuse you.


Change the viewing option from all to a single account. Mobile users may find this trick especially handy since the small screen size makes manual duplicate identification quite difficult. Moreover, the emails you see may not be actual duplicates, you may assume they are. This is a common cause of confusion when people have more than one account configured in the Outlook client and don't maintain a proper folder structure.

Speaking of folders, using them is a great way to manage duplicates inside an email account. That is, if your storage is not an issue.


In the blog, we have learned how to delete duplicate emails in Office 365 account. We learned how to remove replica contacts and calendars. Since there is no direct way to automatically delete these replications from Office 365, the blog suggests that the user can download all the items and then the duplicate items can be removed from the Office 365 file through Microsoft Outlook.


Q. When am I most likely to see duplicate data in Office 365?
A major reason to see duplicate data is after the Office 365 to Office 365 migration. If premigration clean-up is not done properly, then redundant data from the source can end up in the target.

Q. What other places can I find duplicate data in Office 365?
One place where there is a high likelihood of duplicates forming is OneDrive. Moreover, the ones who are on a free plan have a tiny amount of space available in OneDrive. Even people who pay for extra space don't want duplicates to occupy it. That is why it becomes quite important to clear out copies of redundant data from our OneDrive. Luckily for us, Microsoft provides a built-in feature to remove duplicate files. Simply follow these steps as directed.

Q. Are there any cases where I have to manually remove copies of emails on my own?

The automated duplicate detection may not be able to distinguish between certain forms of email. Like in a situation where a person wanted to add an attachment to the email. But they forget, and after a while, a second email with the same content but with the attachment. You might want to keep the one with the attachment and remove the other email. However, even when these types of emails are duplicates, the filter may not consider them as such. Therefore, you have to rely on manual deletion.

Q. I can't delete duplicates due to a reason out of my control. What can I do?
There might be a case where your company policy or industrial regulation requires you to keep 2 copies of the same mail. If this is true, then instead of keeping duplicates in the inbox, make a separate folder for all such items.

Q. What can cause duplicates to build up in Office 365?
The most common cause is when data is imported into a pre-existing account. Other than that, the sender might include your email address more than once for the same mail. If multiple people have access to a mailbox, then it also creates a chance of mismanagement.