1. When you login the Horde Website and see the Mail Maintenance Opertions -Confirmation
You need to click the button Perform Maintenance Operations
2. You need to click the Purge Deleted in order to clear deleted mail in the inbox.
3. Click the Folders, Then click the Trash. then click empty folder
4. Then click yes button to confirm clear the Trash folder.
5. Next click the folder again, then click sent folder, then clear all the sent messages