Guest Account Allows Relaying Regardless of Routing Restrictions

The Internet Mail Service could allow non-authenticated users to relay mail if the Microsoft Windows NT domain Guest account is enabled.

This problem may occur if non-authenticated users bypass routing restrictions that require authentication by using the Guest account. After Simple Mail Transfer Protocol (SMTP) authentication does not work, some clients use the Guest account.

To work around this problem, disable the Guest account. To do so, use one of the following methods.

Method 1

1. Start the Active Directory Users and Computers snap-in. To do so, click Start, point to All Programs, point to Administrative Tools, and then click Active Directory Users and Computers.
2. Click User, and then double-click Guest.
3. Click Account, click to select the Account Disabled check box, and then click OK.

Method 2

1. In Windows NT User Manager for Domains, double-click the Guest account to select it.
2. Click to select the Account Disabled check box, and then click OK to save the changes.