Configuring a single option in Exchange Server 2003 and Exchange 2000 Server can make a big difference in the amount of spam a company receives. If spam messages are being sent to email addresses on your distribution lists (DLs), you can lock down your DLs. Follow these steps:

  1. Open the Microsoft Management Console (MMC) Active Directory Users and Computers snap-in.
  2. Find the DL that you want to protect.
  3. Right-click the DL, and select Properties.
  4. Select the Exchange General tab.
  5. Click the Delivery Restrictions button.
  6. In the Message Restrictions section, change the Accept messages option from the default From everyone to Only from. In the text box, list all the addresses that are allowed to send email to that DL. You can add DLs to the allowed list.
  7. Click Apply, then OK.
  8. Wait several minutes for Active Directory (AD) synchronization to complete, then send an email message from an email address that wasn't in the allowed list to the protected DL. You should receive a notification that states your message couldn't be delivered.
  9. Send an email message from an email address that you included in the allowed list. You should find that the message was successfully sent.

Although these steps are targeted toward stopping unauthorized email messages from outside the company, you can also follow them to stop the abuse of the company email server by employees. For example, you might follow these steps to allow only managers or HR department members to send email messages to a DL that contains the email addresses of all company employees.
—Rajesh Mehta