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Part 9 (DNSBL and SURBL Look-Up Configuration)
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Configuration Options: DNSBL and SURBL Configuration
Settings here are made in the jspamfilter.conf file.
DNSBL Look-Up List
DNS Cache Skimmer Interval
TarPit Setting
SURBL Look-Up List

DNSBL Look-Up Configuration:
Space-delimited list of DNSBLs to use for checking remote IP addresses.*!

If a question mark ("?") is added to the end of the name, the Action will be set to Tag for mail received from servers on that list. If an exclamation point ("!") is added to the server name, the Action for that server is set to Block, and connections from servers on that list will be dropped. If you want to outright refuse connections, use an asterisk ("*" aka "splat") after the DNSBL name. Separate multiple entries with spaces.

Here's a summary of the modifiers for the DNSBLs:

Symbol Name Action Description Additional Notes
REFUSE Refuse connection outright Pre-emptive refusal of connection Cannot be over-ridden by filter file scores. Can be used with the "tarpit" setting (see below).
(Bang/Exclamation Point)
BLOCK Block Connection Dropping of connection: the server drops connections and returns a "550 service not available" error Can be over-ridden by filter file scores.
(Question Mark)
TAG Tag Successful look-ups result in messages being tagged "[JSpamFilter]" tag will be prepended to the subject line of the message.
  Nothing Default Action See also Section 10 on Actions.  

  • Note: Modest Software is not associated with any particular DNSBL maintainer, and many of them ask for a donation in return for use of their services. Some DNSBL maintainers do require payment before you are able to use their services.
  • JSpamFilter checks each DNSBL in the list, and stops when it finds the first match.
  • If you are doing both Blocking and Tagging, you should list any Blocking DNSBLs before any Tagging DNSBLs.
  • DNSBL look-ups are performed before filtering. Therefore, set a DNSBL to BLOCK or REFUSE only when you are certain.
  • Allows the list of domains to be read from either a simple flat file (one domain per line), or from a BIND-formatted DNS boot file. A refresh interval can also be set; JSpamFilter will check to see if the file is updated on that interval, and if so, reload it.
  • The "REFUSE" ("*") setting is stronger than the BLOCK ("!") setting in that values in the filter.txt file cannot over-ride the REFUSE setting. The REFUSE option for DNSBL handling; this setting causes the connections to be pre-empitvely dropped so that messages are not accepted at all.

DNS Caching Configuration:
JSpamFilter can cache positive and negative DNSBL responses for 30 minutes to speed look-ups.

The following parameters set the behaviour, add these lines to your jspamfilter.conf file:

DnsCacheTTL sets number of seconds for time to live

DnsCacheTTL=(number in seconds)

DNS Cache Skimmer Interval
DnsCacheSkimmerInterval determines how often (in seconds) the cache is checked for old entries

DnsCacheSkimmerInterval=(number in seconds)

Tar Pit Configuration:
The following switch makes dnsbl-based drops very slow to slow down spammers; note that this only works with DNSBL entries that use the "splat" (*) value.


SURBL Look-Up Configuration*:

Use a separate line for each SURBL source to be used followed by a colon (":") and the filter score to be associted to the SURBL. That is, if and are the SURBLs you'd like to use with filter scores of 50 and 75 respectively, you would add them to your JSpamFilter.conf file as:

This could take time or increase traffic. *There are several parameters that determine overall performance and the numbers above represent a typical configuration. The buffer size and number of SURBL lookups probably have the greatest impact on message capacity, performance and processor load. SURBL lookups aren't so much a performance load per se, but potentially generate a lot of look-up traffic. The amount of look-up traffic increases with each SURBL used.

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