In Windows 95/98/NT, open Windows Explorer and select Tools | Folder Options. Click the View tab, select "Show all files" and deselect (uncheck) "Hide file extensions for known file types".
In Windows 2000 and XP, open Windows Explorer and select Tools | Folder Options. Click the View tab, select "Show hidden files and folders" and deselect (uncheck) "Hide file extensions for known file types."
The above instructions will display all file extensions except for .SHS files. To display .SHS file extensions, one additional step is required. After following the above instructions, users must then edit the Registry, HKEY_CLASSES_ROOT\ShellScrap, deleting the value "NeverShowExt".
Following is a partial list of file types that should be considered suspicious when received in email and should not be opened unless you requested or expected the attachment: