Consider the following scenario. You use Outlook 2010 and are a delegate for your manager. Even though the DelegateSentItemsStyle registry value is set to 1, an email message that you send on behalf of your manager is saved in your Sent Items folder.
In earlier versions of Outlook, the same registry value forces the email message to be saved in the Sent Items folder of the person on whose behalf the message was sent.
To resolve this problem, install the hotfix that is described in the following Microsoft Knowledge Base article:
2459115 Description of the Outlook 2010 hotfix package (outlook-x-none.msp): December 14, 2010
After you install the December hotfix package for Outlook 2010, to have us enable the hotfix for you, go to the "Fix it for me" section. If you prefer to enable the hotfix yourself, go to the "Let me fix it myself" section.
To enable the hotfix automatically, click the Fix this problem link. Then click Run in the File Download dialog box, and follow the steps in this wizard.
Important After you install the December hotfix package for Outlook 2010 and set the DelegateSentItemsStyle registry value to 1, the functionality is available only when the Exchange account is set to Use Cached Exchange Mode. The DelegateSentItemsStyle registry value does not affect an Exchange account that is configured in Online mode. For more information about enabling Use Cached Exchange Mode, see the following article in the Microsoft Knowledge Base:
The following articles describe this feature in earlier versions of Outlook.
959628 Description of the Outlook 2003 hotfix package (Outlook.msp): December 16, 2008
972148 When you send an e-mail message from a shared mailbox in Outlook 2007, the sent message is not saved in the Sent Items folder of the shared mailbox
Note If you must use Outlook in Online mode and your mailbox is located on Exchange Server 2010, the Exchange administrator can configure similar behavior on the server. Update Rollup 4 for Exchange Server 2010 Service Pack 2 introduces a new Exchange PowerShell commandlet to configure which Sent Items folder a message is copied to. Because this new feature is handled by the Exchange server, Outlook can be configured for Online or Cached Exchange Mode. However, the Exchange server feature only works if the Outlook DelegateSentItemsStyle registry value is disabled.
For more information about the Set-MailboxSentItemsConfiguration cmdlet, click the following article number to view the article in the Microsoft Knowledge Base:
2632409 Messages sent by using the "Send As" and "Send on behalf" permissions are only copied to the Sent Items folder of the sender in an Exchange Server 2010 environment