Briefly, the architecture is built around an application called Outlook and Exchange. The system is built around desktops that have a client through which users access their e-mails. Then inside the data centre there will be servers—computers—that house the data and the application itself.
The data may or may not be—in this case I don't know—stored on multiple servers or backed up in a different data centre, depending on the configurations departments have chosen. So that's the general architecture of the applications.