OUTLOOK SHARED MAILBOX SENT AS 1 Copy IN Sent SHARED MAILBOX's SENT ITEMS ONLY.

Outlooks Application installed on your computer doesn't come with "DelegateSentitemsStyle" already installed into your registry. One would normally have to  Add it to the Registry.

When applying to user registry DO NOT OPEN REGISTRY EDITOR AS ADMINSTRATOR Rather if there are domain user restrictions, it would be better to enter the admin user name and password if prompted. This is how you will find the Preferences folder within the

In specialized mailbox customization such as Having your SharedMailboxes, this registry fix, DelegateSentItemsStyle is for when you want Outlook SharedMailboxes to receive respective Sent item to the sharedbox folder sent items folder instead of the personal inbox sent items folder.

 Computer\HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Outlook\Preferences (Folder)


DUPLICATE OF SENT ITEMS IN OUTLOOK


When I mean duplicate sent items I'm referring to one in Personal Sent  and one in Shared Mailboxes Sent Items, When sent from the Shared Mailbox on behalf 

DelegateSentitemsStyle (Regedit) + Copy items sent as this mailbox & Copy items sent on behalf of this mailbox (365 admin>group> Shared Mailboxes) = DUPLICATE OF SENT ITEMS IN OUTLOOK