Deleted and Sent Items Go From One Outlook Mailbox to Another
Written March 10, 2010 by Ian Matthews

As always, this information is provided without warranty and is based on my own training and experiences. 

If you set up an have an Exchange account with permissions to another account, you may have been frustrated that Deleted and Sent Items from a Mailbox folder of the other account appear in your Deleted or Sent Items folder rather than that of the mailbox owner.   Surprisingly, this functionality is by design under Outlook 2003 and 2007. 

While you can easily "correct" the Deleted Items, there is precious little you can do about the Sent Items. 

One suggestion is to use a second profile in Outlook.  This would solve both issues but it too much of a pain to switch back and forth for most.

SENT ITEMS:  The only thing you can do is drag the Sent messages from your Sent Items to the other accounts Sent Items.  Of course you need to have permission to do that.  I found this unbelievable until I read it directly in THIS Microsoft Knowledge Base article.

DELETED ITEMS:  This is a quick fix.  Simply edit the registry as follows:

1. Go to: HKEY_CURRENT_USER\Software\Microsoft\Office\12.0\Outlook\Options\General\
2. Change DelegateWastebasketStyle entry to 4 (yes, 4.  Set it to 8 if you want it to save in your profile i.e. default)

For a full explanation read THIS Microsoft KB Article.   To make it easier you could just download and install the registry entry HERE.

I hope this helps.