Having an effective antispam and antivirus solution in place in your Exchange Server organization is critical. How you fit these solutions into your Exchange architecture is nearly as important as using the right product.
Since spam reportedly accounts for 90% of all inbound email, it's best to keep it out of users' mailboxes. What's the best way to do that? Ultimately, the best approach is to use hosted filtering.
Hosted filtering points your MX DNS record to a third-party filtering provider that removes spam and sends remaining messages to the Exchange organization. This ensures that Internet bandwidth isn't wasted on spam and that viruses never reach your organization.
While this approach works well, many organizations prefer to deal with spam and viruses locally. In these situations, the best approach is to eliminate spam and viruses at the edge transport server level. Microsoft states that the edge transport server's primary function is spam control. Even so, there are other reasons to eliminate spam and viruses at the edge transport server level.
Exchange Server 2007 uses a centralized hub transport. Every message passes through the hub transport pipeline, regardless of whether the message was sent from the Internet or from an internal user. If you attempt to eliminate spam at the hub transport server level -- or even at the mailbox server or mail client level -- spam will reach the transport pipeline before it's eliminated.
If 90% of all messages are spam and you allow it to reach the transport pipeline, then your hub transport server must process about 10 times more mail than usual. This can back up message queues and affect server performance.
Many small- and medium-sized organizations choose to piggyback the Hub Transport Server role onto their mailbox servers. In these cases, the server's resources may be stretched thin before even throwing spam into the mix.
Additionally, some organizations may be required by law to archive all email messages. Because most message archiving products copy messages as they flow through the hub transport, allowing spam to reach the hub transport pipeline increases archive storage costs. It may also make it more difficult to locate specific messages within the archives, which are congested with spam.
Spam is a nuisance, but viruses are harmful. I recommend scanning for viruses at the edge transport server level. You should also have Exchange-aware antivirus software installed on all mail servers. Finally, be sure that you have antivirus software installed on client machines as well as the appropriate Outlook plug-in.
About the author: Brien M. Posey, MCSE, is a five-time recipient of Microsoft's Most Valuable Professional (MVP) award for his work with Exchange Server, Windows Server, Internet Information Services (IIS), and File Systems and Storage. Brien has served as CIO for a nationwide chain of hospitals and was once responsible for the Department of Information Management at Fort Knox. As a freelance technical writer, Brien has written for Microsoft, TechTarget, CNET, ZDNet, MSD2D, Relevant Technologies and other technology companies. You can visit Brien's personal website at www.brienposey.com.
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