Keeping sent items in the correct mailbox is a common problem for Exchange users who have delegated access to a shared mailbox, or even Send As permissions on another user’s mailbox. Thankfully, there is a solution to this problem, and it works the same whether your Exchange is on premise, or in Office 365.
Any email that a user sends ends up in their own sent items, and not the sent items of the shared or delegated mailbox. This makes it hard to share a mailbox, as you are forever wondering whether an email has been replied to, and you don’t have the conversation history to go back to – very frustrating!
Note that for this to work, Outlook must be in cached mode – if your email is in online (or non-cached) mode, this fix won’t work.
For Outlook 2013:
Edit the following key in your registry:
Create a new DWORD Value:
Name it DelegateSentItemsStyle and set its value to 1.
This fix will also work with older versions of Office, just use the key appropriate to your version below:
For Outlook 2010:
For Outlook 2007:
For Outlook 2003:
Also, if you’re in Exchange 2010, you can set this setting in PowerShell, so that it will take effect not only in Outlook, but in OWA as well. Check this link for more information, but you basically use the cmdlet Set-MailboxSentItemsConfiguration to specify where email is saved once it has been sent. I’m not sure why they removed this from Exchange 2013, because it would be nice to have this globally applied, and not just on a per machine basis, but there you have it… hope this helps someone!