For many companies, the robust messaging and calendaring features offered by Office 365 for enterprises presents an opportunity to transition all messaging functionality from the on-premises organization into the cloud. Office 365 for enterprises includes a full suite of e-mail migration tools.
However, there are dependencies and restrictions on the migration tools that you may be able to use with Office 365. Variables such as your on-premises Exchange Server version, the number of mailboxes you want to move, and how you want to handle user identity will dictate the tools and processes you can use to migrate to the cloud.
Read the complete blog at http://blogs.technet.com/b/exchange/archive/2011/08/29/exchange-server-deployment-assistant-now-includes-a-cloud-only-scenario.aspx
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