Hi, we have a shared mailbox which is shared by several users. When most of the users send a mail from this shared mailbox, it rightly appears in the sent folder of the shared mailbox. However for one user, although mail sent physically from the shared mail box, the mail shows up in the users Sent box and instead of the Sent box of the Shared mail box

Hi,

Which version of Outlook is the user using? If the user is using Outlook 2010, please first install the following hotfix package:

2459115 Description of the Outlook 2010 hotfix package (outlook-x-none.msp): December 14, 2010

After that, add and enable the following registry key in the user's client:

Key: HKEY_CURRENT_USER\Software\Microsoft\Office\14.0\Outlook\Preferences
Name: DelegateSentItemsStyle
Type: DWORD
Value: 1

For more information, please refer:

https://support.microsoft.com/en-us/kb/2843677

Hope this helps.

Regards,

Steve Fan
TechNet Community Support