How to use RBL Servers to block Spam for Free on Mail Servers
In this article we will discuss how to use RBL Servers to block Spam for Free on Mail Servers
First, what is a RBL server? A Real-Time Black List (RBL) is a Domain Name Server (DNS) that contains the IP addresses of SMTP servers that either originate spam, or are considered to be spam open relay hosts. One of the most common methods for sending spam, open relays are servers with insufficient security or other loopholes that allow anyone who knows how to tap into them, and use them for mass mailings of anonymous email.
Fortunately, you can find and use one of several RBL service providers to prevent spam getting in your user’s inbox reject from the start all emails that are sent by compromised spam open relay hosts. This is done by checking the sender’s IP / domain against RBLs
One of the most popular RBL services is SORBS DNSBL. SORBS DNSBL was born in November 2002. It was felt that by publicizing a list of compromised hosts, the ever-increasing flow of spam through those hosts could be stopped. On January 6, 2003, the SORBS DNSBL was officially launched to the public. SORBS provides detailed configuration tutorials
for the most common mail servers.
Another popular RBL service is Spamhaus Block List. The SBL is a real-time database of IP addresses of verified spam sources and spam operations (including spammers, spam gangs and spam support services), maintained by the Spamhaus Project team and supplied as a free service to help email administrators better manage incoming email streams. Incorporating SBL filtering as 1st and 2nd stage filters is explained in the document: Effective Spam Filtering
RBL services are helpful in blocking Spam from Mail Servers but always consider when you intend to block emails using RBLs you could accidentally block legitimate email. Be aware that since blocking can be performed by IP, sometime whole domains get included in RBLs because one subdomain turned out as open relay at one time.
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