This issue is for users who have a shared e-mail account mapped. The sent mail is going into your personal "Sent Items" rather than the shared e-mail account's "Sent Items". Apply the following fix to correct the issue.
- Click Start, click Run, type regedit, and then click OK.
- Locate and then click the following registry subkey:
Note:The x.0 placeholder represents your version of Office (16.0 = Office 2016, 15.0 = Office 2013).
- If DelegateSentItemsStyle entry exists, right-click on it and click Modify. Otherwise, on the Edit menu, point to New, and then click DWORD Value and type DelegateSentItemsStyle, and then press Enter.
- Right-click DelegateSentItemsStyle, and then click Modify.
- In the Value data box, type 1, and then click OK.
- Exit Registry Editor.
- Restart Outlook