With almost all ISPs, you can - theoretically - block email from an individual sender, server, or domain; but getting all the crud blocked without blocking other things you want to get can be difficult.
As a horrible example, Hotmail lets you make a block list, but only if you go in to the website as an html user. I get my email as POP3 from them using Outlook Express, and they ignore settings you make in OE. They are supposed to allow email from anyone in your address book, but they ignore my on-machine address book, and I refuse to give it to them on their web server, so that function is a total null.
Even if you block everything from an entire domain, the borkers have multiple ones they can use.