Mail blacklists

A mail blacklist, also known as a DNSBL (Domain Name System Blackhole List), is a database that contains IP addresses or domain names that are known to send spam or other unwanted emails. Mail servers and email providers use these blacklists to filter out emails from known spammers and reduce the amount of spam that reaches their users.

Here are some popular mail blacklists:

  1. Spamhaus: One of the most well-known and widely used blacklists, Spamhaus has been around since 1998. It has a comprehensive database of IP addresses and domain names associated with spamming activity.
  2. Sender Policy Framework (SPF): SPF is not a traditional blacklist, but rather a protocol that helps prevent spam by verifying the authenticity of email senders. It's used to prevent spammers from sending emails that appear to come from your domain.
  3. DomainKeys Identified Mail (DKIM): DKIM is another protocol that helps prevent spam by verifying the authenticity of email senders. It's used to prevent spammers from sending emails that appear to come from your domain.
  4. Open Relay Blackhole List (ORBL): ORBL is a blacklist that focuses on open relays, which are mail servers that allow anyone to send emails through them, often without authentication.
  5. SORBS (Spam and Open Relay Blocking System): SORBS is a blacklist that focuses on IP addresses and domain names associated with spamming activity, as well as open relays and other types of malicious activity.
  6. CBL (Composite Blocking List): CBL is a blacklist that aggregates data from multiple sources to create a comprehensive list of IP addresses and domain names associated with spamming activity.
  7. PSBL (Pollution Spoofing Blocking List): PSBL is a blacklist that focuses on IP addresses and domain names associated with spoofing activity, where spammers send emails that appear to come from a different domain or IP address.
  8. DNSWL (Domain Name System White List): DNSWL is a whitelist that contains IP addresses and domain names that are known to be legitimate and not associated with spamming activity.

Mail blacklists can be used in various ways, including:

  1. Blocking: Mail servers can block emails from IP addresses or domain names listed on a blacklist.
  2. Greylisting: Mail servers can temporarily delay emails from IP addresses or domain names listed on a blacklist to verify their authenticity.
  3. Scoring: Mail servers can assign a score to emails based on their sender's IP address or domain name, and then use that score to determine whether to deliver the email or not.

It's important to note that mail blacklists are not foolproof, and spammers can still find ways to evade them. However, they can be an effective tool in the fight against spam and help reduce the amount of unwanted email that reaches users' inboxes.