The best way to prevent spam is to use a reliable email service, such as Gmail. There are also 3rd party programs out there that route your emails for you, and do not allow any spam whatsoever to come through, such as SpamArrest. Sometimes, though, you lose valid emails through systems like this, if you do not check the system occasionally. Another way to prevent spam is to not give out your primary email address online, ever. Set up a different account for filling in web forms, as those are typically the culprits that sell off your email address to other companies.