Blacklists usually prevent websites from providing harmful content to the public. ISP's can often blacklist some domains, in order to protect their users. However, sometimes, some domains can end up there when they should't be. Thus, you need to be careful, as your messages can be completely blocked. For example, you can get blacklisted if too many of your emails end up in the Spam folder. Read more about blacklists (and avoiding them) in this section.