Configuring SMTP for Both Authenticated and Anonymous Connections at Microsoft
To reduce administrative overhead, the Microsoft Information Technology (Microsoft IT) group needed to change the way Microsoft® Exchange Server 2003 makes internal Simple Mail Transfer Protocol (SMTP) connections. Microsoft IT set the SmtpIpRestrictionFlag attribute to 1 to configure an SMTP virtual server to allow anonymous connections from an explicit list of IP addresses, yet allow all authenticated connections from other Exchange servers.