When you cant delete a file which
is in your inbox the normal way,
here is what you can do;
1. Install FExplorer.
2. Launch it and goto the path/
folder of your message inbox. If
its on the C drive, it would be C:
\system\Mail001001_S and
the same if its on the E.
3. You will notice there are more
folders, 0 to9 and a to f. Just go
look into all those folders and
you should be able to find the file
that you wanna delete.
4. Once found, click on
Options>File>Delete.
5. Exit FExplorer & goto your
Inbox to delete the file again.