BlackBox describes itself as a consolidated, continually updated database of nearly every email address that is actively being bought and sold on the open market. It is used exclusively by Email Service Providers (ESPs), in order to predetermine if a sender's list is permission-based, spammy, or outright toxic.
Many of the problems that email service providers run into is fly-by-night spammers that purchase a large list, import it into their platform, and then send to it knowing that they had no permission. They know that sending to the list is going to generate a ton of complaints and probably get them kicked off of the email platform – but they're there just to get that first email out. Spamming a list isn't about creating a relationship!
The problem with this is that email service providers have a reputation with the internet service providers (ISPs). If the ISPs see a large complaint ration coming from one of the email servers, they'll block all the email coming from that server! That means that every client that has email sending from that server is impacted… that could be you!
Using a service like BlackBox intelligently, I'm confident that a sender could predict the risk associated with a new client coming on board. ESPs have to be careful, though. I had an ESP once tell me my list was past a threshold and I had to argue with them. Even though I hadn't bought a list, there were enough email addresses on my list that matched one of these databases that I was flagged as a spammer – DESPITE the fact that I had permission and had been sending for years. They eventually relented, I sent to my list and my complaint rate was 0%.
Remember, this is not a database of email addresses that are not deliverable, nor is it a list of email addresses that explicitly don't have permission. It's email addresses that are commonly bought and sold by email list services. I'm quite confident my email address is in Blackbox… but I actually do subscribe to hundreds of newsletters.
This is a valuable service to any ESP that is having problems with spammers destroying their reputation!