While Office 365 and Exchange Online are all the talk in the messaging world, there are still a lot of mailboxes in the data center. Most estimates say there are more Exchange mailboxes running on premises right now than there are in Office 365.
Exchange Server's importance to your organization means it's crucial to hone your abilities to diagnose a problem when an outage occurs. Every issue is different, but there are some common problems that can be fixed with some Exchange troubleshooting tools to get the system back up and working in short order.