We're having problems with open relay on Microsoft Exchange Server 2000. We tried to shut down\u00a0 SMTP, clean out queues, turn off relaying, etc., but nothing worked. For a quick fix, we set up a temporary mail server using Mdaemon. Is there a less drastic way to close the open relay on MS Exchange Server? How do we prevent this?Exchange relaying has received a lot of attention lately. Two\u00a0Microsoft\u00a0security bulletins about the troubles are: Microsoft Security Bulletin -\u00a0MS02-011, Authentication Flaw Could Allow Unauthorized Users To Authenticate To SMTP Service; and Microsoft Security Bulletin\u00a0MS99-027, Encapsulated SMTP Address Vulnerability. If your server is falling victim to authentication spoofs, closing the open relay might not stop the spam. Patch your Exchange server with the latest fixes and service pack, then open up the Internet mail service and choose routing. Under Routing Restrictions, turn on "host and clients with these IP addresses" and leave the list empty. More information is available from Microsoft (details here). You can test your mail server using telnet to Port 25 after making your changes to verify you can't send relayed mail.