At around 3:45pm, users started complaining that our mail server wasn't responding and sure enough, it wasn't! I quit and relaunched the server app, EIMS Server, even though it seemed fine but still no response. Our Internet servers are all networked off of our firewall's DMZ port and so I tried pinging our FTP and Web servers and they weren't responding either. Our servers were unable to access external sites too. So I tried rebooting our firewall but still no response. The problem turned out to be a mini-switch (the one that all our Internet servers are connected to) that had "hung" due a super-brief electrical outage (the lights on our whole floor flickered for a split second). I cycled the power on the mini-switch and that did the trick! Phew!