- Misconfigured Rules: There might be cases that two or more rules are fired upon receiving email, resulting in multiple instances of the same messages.
- Synchronization Issues: We have also observed duplicated contacts and messages resulting from sync problems with 3rd party providers.
- Send/Receive intervals are too short. If the frequency of your inbox update is too short; Outlook might load the message into your inbox, BUT might not be able to mark messages occurrences as synchronized/loaded. This results in multiplied occurrences of the same messages.
- Incorrect Account Setup: Mistakenly defined multiple occurrences of the same email account can result in multiple instances of each incoming email, contacts and calendar entries.
Solving Email Duplication
1) Misconfigured Rules: Under Rules > Manage Rules & Alerts, ensure that multiple rules are not firing in parallel for each incoming message.
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2) Synchronization Issues: If using 3rd party web email providers, Check that your GMail, Yahoo and Outlook.com accounts are correctly defined in Outlook.
3) Send/Receive intervals: Decrease the frequency of your inbox update. Here’s the step by step process:
- In Outlook, hit Send / Receive
- Hit Send / Receive Groups
- Select Define Send / Receive Group
- Set the time interval to a value between 15 and 30 minutes
- Click OK.

Cleaning your inbox
To clean up instances of duplicate mail go to "Clean Up" under the Home tab and select "Clean Up Conversation".

- Clean up folder will delete and move duplicate emails in the specific folder to the Deleted Item.
- Clean up folder and sub folders will allow you to clean up also subfolders.
- Once done, you might right click on the Deleted Items folder and hit Empty Folder to delete your duplicated email instances for good.