Before people slam me for not doing something obvious to them, I'll preface this story by saying I am in no way a network admin. I'm just the guy who knows the most about computers in a small company.
One morning I load up Thunderbird and start downloading my email. I see about 100 emails with the subject line "<font size="-1">YOU HAVE REACHED YOUR DAILY SMTP RELAY LIMIT". Oh. Shit. We've never reached our limit, or even come close before, this can't be right. I log into our server and bring up the list of emails queued to be sent. It's gigantic. Ohgod-ohgod-ohgod-ohgod. Someone hacked our server and is using it to spam. They've used up all of our relays and now none of our emails we send will go through! What the hell do I do?!
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<font size="-1">I've been so careful to enforce strong passwords and to sanitize all webpage inputs. Ohgod-ohgod-I'm sweating, I'm gonna throw up. I'm going to have to format the server and spend countless hours getting everything back up while the entire company grinds to a halt. I'm so fired.</font>
<in walks one of the owners>
owner: Hey, so Bill sent out a few thousand (unsolicited, read: spammed) emails late last night, I think that'll help with some extra sales. He has the entire student directory for State University (40K+ people) and is emailing (read: spamming) all of them, too. Isn't that awesome?
me: ...........what.
My hyper-ventilating didn't stop immediately. I had to then explain how absolutely ridiculous, and illegal, that is. Then explain to them that everyone gets to use their personal email accounts or to make a hotmail account to send email from until the relays are back in order. This crowd probably won't be surprised that the conversation wasn't as simple as them just understanding and agreeing. The owner's solution was to increase our SMTP-relay limit.
In the end we all agreed to stop, and that I get to kick Bill in the face when I see him. But I'll never forget that terror - over nothing.