This has been a big design issue with Outlook. Following are the issues.
- When you have multiple mailboxes and send from a secondary mailbox, the sent item gets saved in the default mailbox of Outlook profile.
- If the mailbox is shared between multiple people, it is hard to keep track of sent communication by that one mailbox.
To fix this issue two things need to be done.
1. Apply the hotfix below
2. Apply the following registry settings.