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Combatting Spam

There are an increasing number of ways which ISPs and Internet hosts are employing to combat the spam problem. Most of these measures are technical-social hybrids and rely heavily on the reporting of spam received, a difficult task to do on large systems.

Black-Hole Systems

Black-hole systems make use of a continually updated database of email addresses or open email servers that are exploited by spammers. Incorrectly configured mail servers are open to abuse by spammers and often the systems administrator isnt even away the abuse is taking place. By using a black-hole system, the mail server (upon receipt of a message) will check to see if it comes from a listed problematic system by querying one of the various anti-spam databases around the world. This requires careful configuration of the mail server as some black-hole systems are too strict and result in legitimate email not getting delivered. Others exist for only short time, terminating once funding runs out which means the database no longer gets updated and as time passes the information in the anti-span database will rapidly become obsolete.

One of the advantages of a black-hole system is that the mail server rejects problematic emails before they are accepted for delivery. This prevents bandwidth wastage from occurring.

Another advantage is that it is possible to use multiple black-hole services available, from the free to the commercial. This means that no one database has to have a complete picture of where spam is coming from, and by using multiple servers more spam can be caught before it gets delivered.

The disadvantage is that black-hole systems require regular administration. Black-hole databases go offline fairly often and dont come back online at all sometimes. In addition, the black-hole system itself requires stringent oversight. False positives are regular and the database needs to be able to accurately keep up to date daily. Most black-hole systems are also free services relying on third party funding and assistance with keeping the database current. This places the burden on users of the system to monitor the spam they receive and report spam messages complete with message headers.

Realtime Blackhole Lists (RBL's)

An RBL is a regularly maintain list of IP addresses that have been shown to send spam as well as those who support the sending of spam (i.e. offering services to spammers, or allow their resources to be used by those who send spam). Various online services exist which offer RBL lists for commercial or free use.


iWeek 2009

iWeek 2009 conference and exhibition,
Bryanston, Johannesburg,
2-4 September 2009.

Please contact ISPA for sponsorship and exhibition queries:
iweek (at)

Report Internet child pornography to the Film and Publication Board's hotline or the SAPS. More info here