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 : DNSBL Support
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JSpamFilter can perform look-up queries to DNSBLs to determine if incoming mail is being sent by a server known to send spam email.

There is a type of list called a DNSBL, for "DNS Spam Blackhole List", that is made available on the Internet as a source of information on senders of spam email. There are various groups that maintain these lists*.

These lists consist of the addresses of servers that have been observed to be sources of spam email. These servers are identified either as being misconfigured to relay messages without question (this is done through completely accurate mechanical tests), or determined to send a significant amount of SPAM compared to overall message volume.

Unfortunately, many mail servers do not support these blacklists, or have very weak capabilities for handling mail with suspicious content. JSpamFilter is designed to add these features to any SMTP mail server.

Based on the settings made by the Administrator, JSpamFilter performs look-ups of incoming email connnections to determine whether the remote mail servers are listed on the DNSBLs the Administrator has chosen to use.

If the IP address or the associated domain of the sending mail server is not listed on a DNSBL, JSpamFilter proceeds with the content filter analysis.

If the IP address or the associated domain of the sending mail server is listed on a DNSBL, JSpamFilter performs one of three actions:

  • Refuse the Connection Altogether
  • Allow the Connection But Refuses the Message and Send the Message Back to the Sender
  • Tag the Subject Line of the Message with "[JSpamFilter]"**
The various DNSBL lists are maintained by independent groups which have different criteria and procedures for determining whether a domain or IP address should be associated with spam sendin parties.

Because of this, JSpamFilter is structured so that the Administrator determines which DNSBLs to use and how JSpamFilter should react if a look-up on that list is positive. This is discussed later in User-selectable choice of DNSBL and strength of response

See also the following sections:
*Access to the information on some of the lists may involve a fee. ModestSoftware is not affiliated with any DNSBL maintainer. If you use a particular DNSBL, ModestSoftware encourages you to support the maintainer of the list.
**The message then continues to the Content Filters where the score can increase so that the resulting message score exceeds the Block Threshold and the message is in fact blocked.
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