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If you've used Outlook Web Apps with on-premises Exchange, then you'll find the online OWA that's part of Office 365 very familiar.
Exchange Online gives you the tools to take control of mail flow inside your business, managing server rules. You can also use Forefront Online Protection to add additional anti-spam and anti-malware controls.
Regulated industries need to be able to prove that they're working within the appropriate framework. You can use Exchange Online's auditing tools to provide regular reports, online or via email.