This update addresses the 'Windows 2000 SMTP Mail Relaying' security vulnerability in the Windows 2000 Simple Mail Transfer Protocol (SMTP) service and is discussed in Microsoft Security Bulletin MS01-037. Download now to prevent malicious users from relaying e-mail messages from your computer. This vulnerability results because of an authentication error in the Windows 2000 SMTP service that installs by default as part of Windows 2000 Server products and optionally on Windows 2000 Professional. Download now to prevent a malicious user from using your computer for mail relaying. This vulnerability applies only to standalone computers (a computer that is not a member of a domain) and does not affect computers that are running Exchange 2000 Server.