Free tip: buy a domain name from a registrar that offers free domain forwarding (mine costs $1 per year). From there, you can create as many different addresses as you want under that namespace, redirecting all mail to your inbox. If you wanna cut off all communications with a group of users, delete the forwarding address and it's gone.
I do exactly this! But it's a little outside the reach of a lot of people, unfortunately. I also think that it would be a less effective tool if more people used it (and thus corporate policies and spammers found it worth tailoring algorithms to the model).