Throttling Policies and Exchange Online…
Throttling policies in Exchange Server 2010 have been an often discussed and much misunderstood part of Exchange over the last few years. Especially with Exchange Online! However, Michael Mainer has written a great article about Exchange Throttling policies on his blog.. well worth a read if you want to understand what all of those policy options really do 
Neil Johnson [neiljohn@microsoft.com] Senior Consultant, Microsoft Consulting Services, UK