Unfortunately SPAM is inevitable these days. I have nearly solved the problem by using a program called Mailwasher but it is not free and it works by looking at the emails before they are downloaded and analysing them. After a while it learns what is good and what is bad and you can set it to delete automatically. There are several other similar programs out there but this is the only one I have tried and it works well for me personally.
Also some email programs have filters built in that you can set to refuse emails from some sources.
It is a pain isn't it.