We do not allow for Corporate emails to be downloaded to PCs/Macs outside of the building. This is the default for Windows/Outlook (i.e. you have to explicitly enable RPC/HTTP, Outlook Anywhere, etc to enable external Outlook clients). It appears that Outlook 2011/Mac circumvents these controls (presumably since it works through OWA) and allows external users to connect to and download local copies of Corporate emails.