I actually send an email to a fake address I know doesn't exist, then when I get the "sorry, fatal errors, the server hates you, don't send stuff" email, I copy it, change the details, and then email that to the person who won't take me off, and generally, they will get tired of hearing that my email "doesn't work" anymore and delete my address. Either way it proves how much of an annoyance it is to me without really saying it bluntly to the person's face. Call it passive-aggressive, call it social engineering, call it shallow, but I call "blame the server." Works great.