Govtech.net has a podcast about Exchange security available freely (requires registration) - Exchange Security: A Quick Primer.

ABSTRACT: Today’s complex Exchange environments are costly and difficult to protect and secure from threats like spam, spyware, malware and viruses. This 12-minute expert Podcast features a summary of the key issues pertaining to the security of Microsoft Exchange in enterprise environments.
Download this expert Podcast and learn how to secure your company’s Exchange environment and reduce downtime and lost productivity due to attacks on your messaging system. Listen to this expert Podcast anytime and learn how to:

• Secure your company’s Outlook Web Access
• Handle spam with Exchanges’ intelligent message filter
• Secure remote clients with RPC over HTTPS instead of VPN
• Control Exchange message delivery
• And more

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