Over a two day period, I spent a total of about six hours working on our church's server to make it do a better job filtering spam. This all started because one of the persons on that domain started getting literally over 300 spam email messages per day.
That's basically one every five minutes, although I swear that when I was monitoring the mail logs, it was even more often than that.
In the end, I wound up IP blocking a bunch of them, then using about three different spam filtering approaches on the mail that did get through. That's reduced the flow from 300/day to about 20/day -- which is still stupid, but at least not completely overwhelming.
Here's a quote from the web site of one of the companies that was flooding the server (until I banned their IP block): "Email marketing is why we get up in the morning. No joke. No hype. We love what we do. And so will you." Umm ...
I would like to find some of these spammers and bill them for six hours of my time. It's one thing when I spend six hours on the church web site, making it better, because then I am adding some value to the world. All I did with this six hours is take back some of the value in the world that the spammers stole.