What are blacklists?

Blacklists help prevent spammers

All spammers are fly-by-night operators. To prevent that from happening a lot of publicly available blacklists (300+) have been created. They are used by various mailbox providers and filtering software to varying degrees.


There are two types of blacklists:

  1. Domain Based

The blacklist looks for domains in email body which have been a known source for spammers. These domains will not be just in an initial link but in the final redirected link too.

Some of the examples are: - SpamHaus DBL - URIBL

  1. IP Address Based

RBL and DNSBL are used to identify whether the IP of the sending server is an open relay or has been used by spammers or is by an ESP which allows spammers to use their infrastructure.

Some of the common ones are:

  • Return Path Reputation Network Blacklist (RNBL)
  • SpamHaus Blacklist (SBL)
  • Exploits Blacklist (XBL)
  • Composite Blacklist (CBL)
  • SpamCop Blacklist (SCBL)
  • Passive SPAM Blacklist (PSBL)


Checking that your domain and sending IP is not in any of the blacklists is one of the first measures which you should take.