If you're asking questions like this, it's clear you don't manage your own mail and these are questions you should be asking whoever does manage it.
Say you're getting mail at @plook.net, then you need to go to the plook.net admin and ask him if anything can be done about the spam. If he says no, then there's very little you can do server-side. If you get mail from your internet provider, and you get too much spam, it's time to tell them you've had enough and they're going to lose you as a customer f they don't fix it.
However, if you don't run your own mail server, the best way to get rid of spam is to move to Google mail.