Hello Mohammed Maged
Good morning!
Thank you for publishing in Microsoft Community. We are happy to help you.
Based on the description you want to remove duplicate emails from your inbox, because it makes your mailbox full.
It's important to know the type of account you're using, because each account has a different process and a different support category.
What type of account is affected? is outlook.com account, Hotmail account, or professional/educational account.
However, to better understand the problem and provide a solution, we need more details from you, please provide us with the following information. Thank you.
A- This is a manual method with which you visually compare messages and decide for yourself whether to delete them or not.
Change the view of the selected Outlook folder to the "Preview" mode.
In the View Settings menu, click the Columns... button and define the columns to display by pressing Add.
Then click on the header of the desired column, for example, "Size", to compare messages and remove duplicates.
In the View Settings, you can click the Sort... button to sort messages by subject, time of receipt, sender, etc.:
View > View Settings > Sort...
In the "Sort" window, select the comparison parameters from the drop-down lists one by one and click OK.
Click OK in the "Advanced View Settings" dialog box to save the sorting settings.
Now the messages are sorted by the selected parameters.
Select and delete duplicates.
This is a tedious method of removing duplicates. You must constantly compare message data and decide which message is redundant and which is not. You have to think about which ones to delete and keep. This method is good if there are few duplicate emails, and you know which folder they are in. But if you have a large number of duplicate emails in different Outlook folders, it will take too much time to find, compare and delete them manually.
B-You can use PowerShell command to deleted duplicates emails. You need to be admin or contact your IT department for helps.
This allows the script to run against mailboxes in Office 365, and then you can remove duplicate messages by running PowerShell, please kindly refer to the following commands.
Remove-DuplicateItems.ps1 -Identity olrik@office365tenant.com -Type Mail -DeleteMode MoveToDeletedItems -Mode Full -Credentials (Get-Credential) -Retain Oldest
In advance, please kindly check this official document to connect 365 PowerShell Connect to Microsoft 365 with PowerShell - Microsoft 365 Enterprise | Microsoft Learn
C- Please from my opinion full and you are not receiving emails issue, can be related to Mutiple cause so go to you outlook on the web and check your issue and check the storage of your mailbox and let me know.
4-Do you want to keep the old outlook? if yes! it is possible to keep the old outlook
We look forward to your reply. This requested information will help us narrow down the scenario and find the right troubleshooting. We will continue to assist you based on the information you provide. I sincerely appreciate your patience and cooperation.
Sincerely
Eben Ezer Tres | Microsoft Community Moderator
