SpamFilter - Network Tests
Overview
The Network Tests feature of SpamFilter enhances SpamFilter catch rates by accessing external network resources such as databases containing the IP address of known spammers and compromised systems, and Real-Time Blacklists (RBLs).
These external resources give an added advantage over simple keyword and rules-based spam filtering, as these lists are frequently updated by anti-spam organizations worldwide. Using Network Tests in combination with standard SpamFilter scoring and the new DIA RBL architecture creates a comprehensive, effective, and always up to date method for catching spam.
Configuration
To use Network Tests, access the SpamFilter -> Network Tests menu option. Simply check 'Enabled' to turn this feature on, and set a reasonable timeout. The default timeout is 10 seconds, which works well in most scenarios.
You will also have the option to customize which Real-Time Blacklists (RBLs) are used by switching the Real-Time Blacklist Settings option from 'Recommended' to 'Custom'. Simply select or de-select the RBLs you wish to use or remove.
Troubleshooting
You may find that enabling this feature or changing the default settings causes your unit to become sluggish, or raises the system load to high levels. Under normal circumstances, you should not experience this problem with the recommended (default) settings. If you find that is not the case, you can reduce system load in the following ways.
The first is lowering the Network Tests Timeout option. We recommend 10 seconds, but if the tests are taking too long to run, mail will have trouble flowing smoothly, thus contributing to high load as new messages come in to be processed. Try reducing this timeout by a second or two incrementally until you find a setting that stabilizes the load.
Adding extra RBL checks outside of the default set may cause load issues for the same reason. The greater the number of RBL lists a message is checked against, the longer it will take to process. In situations where a large volume of mail is being processed, even a few extra seconds for each message can turn into a significant strain on the system. If the default settings seem to be generating too much system load, try reducing the number of RBL lists being checked.
Another potential problem causing high load and/or slow email processing could be caused by slow or non-responsive DNS resolvers. Testing DNS servers with a dig or nslookup command should be completed to assure this is not the problem. DNS servers can be changed in the event they are slow or non-responsive under the ISP Settings (WAN) page under the Network menu.
