Sendmail 8.9, the latest version, comes locked down against relaying right out of the box: you can find out more about previous versions by going to the Sendmail web site (Resources). So rather than focusing on initial configuration, let's look at a more insidious problem: taking over someone else's Sendmail setup and making sure they haven't punched any holes in it spammers might use.
Don't roll your eyes. There are a lot of administrators who just kind of fell into their jobs, and rather than learning the proper way to do things will punch security holes to get their workarounds to function. Maybe you were even one of them once, but now you know better, but you've forgotten to go back and clean up all of your old messes.
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