If your organization restricts computers on your network from connecting to the Internet, you should allow outbound connections, also known as whitelisting, to ensure your computers can successfully use Office 365 Using URL whitelisting is the recommended approach due to the modern web architecture of Office 365.
While IP whitelisting will work, there are a number of downsides to this approach, including:
Web clients such as the Office 365 admin portal or Outlook Web App won’t be able to authenticate.
Future non-web based clients may not be able to authenticate.
Additional Office 365 infrastructure won’t become instantly available to client computers.
Updates will be required as frequently as weekly.
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The updated article is on – http://technet.microsoft.com/en-us/library/hh373144.aspx
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