A number of users are experiencing problems with Windows Mail and deleting messages from the Inbox and Outbox. The message will first become unviewable in the reading pane and will then generate an error when you try to delete it. This is usually caused by a corrupt mailstore. To rebuild the mailstore (WindowsMail.MSMessageStore), follow these steps:
1. Back up the email you wish to keep. While rebuilding the mailstore shouldn’t result in any loss of email, it is always better to be safe.
2. Close Windows Mail.
3. Click the Start Button and select Computer.
4. Navigate to C:\Users\your username/AppData/Local/Microsoft/WindowsMail.
5. Delete WindowsMail.MSMessageStore.
6. Open the Backup directory.
7. Open the new directory.
8. Delete WindowsMail.MSMessageStore.
9. Open Windows Mail to rebuild the mailstore database.
You should now be able to view and delete the problematic message(s).