A very interesting & recommended web cast, which every Microsoft / Exchange guy should watch, Mrs. Luisa Garcia, Microsoft IT Service Manager, is describing that how Microsoft transitioned his Messaging System to Exchange 2010.
Check out this Web Cast:
https://msevents.microsoft.com/CUI/WebCastEventDetails.aspx?EventID=1032448860&EventCategory=5&culture=en-US&CountryCode=US
Zahir Hussain Shah
Azure Hybrid & Cloud Migration Blog 
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