If you suddenly experience problems with email such as bouncebacks explaining your IP address is blacklisted, this is usually due to the fact that you have inherited a bad IP address from your ISP. Most internet providers assign a dynamic IP address (this means that everytime "you log on" to the internet you receive a different IP address) and therefore it is possible that the user using that IP address before you may have been "spamming the world", therefore that IP address gets blacklisted.
We recommend paying for a static IP address to eliminate this problem. Any further advice please contact your ISP.
Handy link : http://www.ripe.net