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How to use a DNSBL
DNSBLs are easy to use from a query perspective. All you need is a script or piece of program code to lookup the IP number of a hostname.
What Happens:
Each DNSBL zone has a domain name, if example.com run a DNSBL with a zone called block they will typically have a domain name block.example.com which 'contains' the zone.
To test whether an IP is listed in their zone you simply reverse the octet numbers (a.b.c.d becomes d.c.b.a) and append the domain name to the result (a.b.c.d becomes the composite domain d.c.b.a.block.example.com).
If the international DNS system contains an entry for that composite domain name then the IP is listed.
Administrators:
Most email servers come with settings or add-ons that will do this lookup for you, simply give them a list of the DNSBL to check and some actions to do if the check is true.
See the documentation for your server software for more detailed help.
Home Users:
End-Users, Joe and Anna Bloggs do not usually have the benefit of running their own email server so they have a more limited set of options. Although the range of anti-spam products for home users are increasing.
What is needed, is either an email client which has a built-in RBL check settings. Or a relay, much like a firewall which sits between their ISP mail server and their home email program.
Tools NOT recommended are:
- MailWasher - Causes 'bounce' attacks on other users
- SpamArrest - Run by a spammer organisation
- Anything saying it does 'Challenge-Response' filtering. - They are attacking everyone else who has had their email address forged in a spam. Also they are known to produce DDoS attacks (infinite loops of challenge bounces) that can shut email servers down.
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