Alison Gootee: Understanding Blocklists

Do blocklists matter? Are you going to have deliverability troubles if your sending IP address is on a blocklists? It's a complex question, as the nature of blocklists and their usefulness has evolved over the years. They were a prime part of the spam filtering equation many years ago, but nowadays, most mailbox providers utilize their own filtering more heavily than relying upon DNSBL-based reputation data published by third parties.

And this is perhaps reinforced by the fact that my "Blocklist Resource" website over at has turned into a sort of blocklist graveyard, where I've documented the shutdown of more than two dozen anti-spam blocklists over the years. Including, most recently, SORBS.

Indeed, historically, most blocklists were a very binary measure of reputation, where it was often the case that a single spamtrap hit, or small number of spamtrap hits, would be enough to blocklist an entire IP address, or even perhaps a whole network range or email sending platform. But for most, the reputation equation has evolved. Whether or not to block now involves a lot more data points -- that equation is much more complex than it was when I first started my own DNSBL in the late 1990s. And thus, it is really no longer true that finding your IP address on a blocklist means that you're going to have trouble delivering email messages to the users at a big mailbox provider.

But, exceptions still exist. There are some instances where certain blocklists do matter. So it can't hurt to learn more -- and that's exactly what I've got for you today, courtesy of Alison Gootee from Braze. Click on through to read her excellent article, "Deliverability Indicators: Understanding Email Blocklists and What They Mean For Customer Engagement."

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