Dns realtime blackhole list7/1/2023 However, most mail server programs cannot see the difference, so it doesn’t really matter for the simple decision if we will accept a connection (= no entry) or not (= 127.0.0.x).įor testing purposes to check if the list is active and working, a 127.0.0.2 test record should be there per convention. Entries may be grouped in such way that different 127.0.0.x may designate different classes of entries like spam sources, open relays, spam support sites, DULs, etc. The 127.0.0.x (the x to be greater than 1) is freely choosen by the zone maintainer. Please note the reversed notation of the IP address octets (ip4r) as the address is translated into an articifical subdomain name. Note: all domain names and/or IP addresses given in this arcticle are just examples and unrelated to the real world. IN TXT "My-private-blacklist: test record. IN TXT "confirmed DUL range, please use your ISP's smart mail host"Ģ.0.0. The “positives” entries in that zone file (following example in BIND format) are A records and TXT records like 44.3.200.10. These BLs are just a list of spam-related IP addresses, implemented as a DNS zone file, so that the list can be easily queried by simple and fast DNS lookups, and hence the name DNSBL. The mailserver checks the IP address of every incoming SMTP connect request against one or more DNSBLs = DNS based black lists. Since MAPS went commercial and RBL is now a service mark of MAPS LLC, the generic term DNSBL is preferred over RBL or DNSRBL in this article. The first DNSBL was the MAPS RBL (Realtime Blackhole List) by Paul Vixie in 1997. One of the most efficient ways to block mail spam is to do it on mail server level by denying incoming connects from spam sources, where the contacting remote machine is identified by its IP address which is checked against one or more DNSBLs on the fly. A DNSBL is a DNS based blackhole list, which can be used as countermeasure against unwanted mail spam.
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