Use Restricted Distribution Groups
As mentioned previously, many strategies for blocking spam also help in slowing or stopping the spread of viruses. Another effective deterrent against spam is to use restricted distribution groups in your Exchange organization. A restricted distribution group allows only authenticated users to send messages. This restriction is especially important because, if spammers know the alias of a distribution group, they can reach many of your employees with a single e-mail message. Restricting distribution groups is especially effective for large lists that contain many nested distribution groups.
Note
Be aware that many spammers use dictionary attacks as a mechanism to reach recipients. A dictionary attack uses software that opens a connection to the target mail server and then rapidly submits millions of random e-mail addresses. This technique is effective because distribution groups are frequently represented by an alias that is a common word.
For detailed steps, see "How to Set a Distribution List as Restricted" in the Microsoft Exchange Server 2003 Security Hardening Guide.
Resource
- For more information about restricting submissions to distribution lists, see "Securing Your Exchange Server" in the Exchange Server 2003 Transport and Routing Guide.