blank mail got in Exchange server

All most all users has get blank mail in Exchange server.
Message “SUBJECT/HEDDER” is readable but message content/text/data is unreadble/blank.

Server & OS Detail:

OS: Windows Server 2003 Pro. with Service Pack 2.
Exchange Server 2003 (Ver:6.5)with service pack 2.
Exchange Server 2003 Component is already installed.