What is a Blacklist?

This is the first article in a multi-part introductory series on blacklists and blacklist activity.

A Realtime Blacklist, or RBL, is a list of IP addresses and domain names that an organization has decided to block, typically for spam.  There are many Blacklists, and each focuses on different types of undesirable behavior.  For example:

  • CBL or Composite Blocking List is a DNS-based blackhole list of suspected e-mail services sending SPAM email resulting from virus or malware infections.
  • Listing on Backscatterer blacklist indicates that your server is issuing “backscatter” in the form of Non-Delivery Reports (bounces) to external users, or misdirected autoresponders and sender callouts.
  • Inclusion in either of the MAILSPIKE Blacklists (BL or Z) means that your IP Address has most likely been identified as being part of a real-time spam outbreak.

Blacklists are typically used to block undesirable internet traffic.  For example:

  • Blocking access to websites on domains known for malware
  • Blocking incoming email from IPs or domains known to be spammers
  • Blocking access to IP addresses based in risky countries

MxToolbox does not own or operate any of these blacklists.  Instead, our email experts curate a list of over 100 blacklists and aggregate blacklist information into a single, central lookup tool.  Our tools enable you to check your mail server IPs and domain names against all these blacklists in a single consolidated interface.  Our monitoring packages enable you to monitor your domains and IP addresses for blacklist activity and get instant notification when placed on a blacklist.  We built our lookup and monitoring tools to help you navigate the complicated world of blacklists.

Your email deliverability depends on staying off of blacklists.  Get protected today.

In our next installment of our series on Blacklists, I will discuss how legitimate businesses sometimes end up on blacklists.