Email blacklists (also known as blocklists or block lists) are everywhere. They rank from the formidable to the obscure. The exact number of blacklists is not fully known – there are at least hundreds. Reputable blacklists carry weight amongst the email receivers of the world and can negatively impact delivery, while other, more obscure blacklists hold little sway and do not have much of an impact on a sender’s ability to get in the inbox.

With so many blacklists out there, being listed is usually a question of when and not if for most marketers. To put it bluntly, Blacklists Happen. So which blacklists should you most be concerned about and, more importantly, how can you stay off them? Let’s take a look.