Firstly if you have no idea what the Microsoft Security response Center is then have a look at this URL.  

http://www.microsoft.com/security/msrc/default.mspx

They even have the 10 immutable Laws of Security

http://www.microsoft.com/technet/archive/community/columns/security/essays/10imlaws.mspx?mfr=true 

If you havent got time to sit one of the Premier workshops or prefer to learn on your own here are all the links for webcasts and virutal LABS for Securing messenging

http://www.microsoft.com/technet/security/learning/messageinfrastructure.mspx 

If that whet your appetiate then there is a whole list security related pages can Vist on the

http://www.microsoft.com/technet/security/learning/default.mspx 

External threat

http://www.microsoft.com/technet/security/learning/external/all/default.mspx 

Improving the Intelligence of Your Gateway Security

http://www.microsoft.com/technet/security/learning/gateway.mspx

Securing Internal and External Access to Corporate Resources

http://www.microsoft.com/technet/security/learning/securingaccess.mspx