It is important to understand to ramification of having your site hosted on a shared server that has sites that are black listed. Sites can get black listed for many reasons but the most relevant is being a spammer.

If your site is on a shared web site server with other websites that are black listed, your site will also be black listed due to having the same ip address.

To avoid this scenario you may want to check your domain or ip  address. If you find your site is black listed you may want to find a new web host company.