Advantages: Can block messages coming from known servers that transmit spam.
How it works: There are lists available on the internet that list open relay servers. These types of servers allow any user to send messages through them. It is highly likely that spammers will send messages through these servers and many of emails coming from this server are spam.
Limitations: There have been several cases of legitimate email servers being added to these lists and some of these servers also pass legitimate email messages. So there is a chance that a message you want to receive could be blocked by these RBL lists. Using this filter can slow down SpamBully processing as it must check each message IP address at several remote servers.
Recommendations: If you are having a problem with too many spam messages passing through SpamBully and you have a high speed internet connection, you can enable this filter to help filter more spam. If you have a slow connection, you can test it for speed and effectiveness in filtering your spam.