You make it socially unacceptable to run a server that emits spam. You make it socially unacceptable to work for a company that emits spam.
At an interview: "OK, I see you worked for an oil company, right, and then a porn company, fine -- oh, you worked for a spammer. Sorry, we're done. I don't know how this happened, I'll need to talk to HR about their filters."
socially where? where ever you set those social norms, someone will set up a server not there. like russia or any of the other internet bogeymen countries
At an interview: "OK, I see you worked for an oil company, right, and then a porn company, fine -- oh, you worked for a spammer. Sorry, we're done. I don't know how this happened, I'll need to talk to HR about their filters."