Does Gmail use Spamhaus? Or any other blocklists?

This is a question I get a lot. Does Gmail use any blocklists? Or, somebody will tell me that they're having Gmail issues, and they've plugged their own IP address into an online blocklist lookup tool, and they are sure that any results found (blocklisting issues) must somehow be part of the underlying cause of their deliverability woes. Except, that's just about never the case. Here's why.

There are a zillion blocklists out there. Speaking specifically just about DNSBLs (IP-based blocking lists), there's a good 90+ of them. But blocklists are a bit like blogs,  in that anybody can publish them and the fact that it's been published doesn't mean that anybody is guaranteed to be actually looking at the what has been published. The net here is that there are a lot of blocklists that, if your IP or domain ends up listed by them, this does not mean that you're suddenly going to have significant deliverability issues at any of the biggest mailbox providers.

The one exception to this is Spamhaus. Spamhaus is broadly respected and as a result, they're broadly subscribed to. Meaning, if your sending IP address ends up on the Spamhaus ZEN blocklist, an email marketing sender is likely to see bounce rates spike significantly. Tons of mail services use the Spamhaus blocklists to filter or block inbound mail, and that includes the biggest mailbox providers: Yahoo,, Comcast and many others will reject your mail, if you're blocklisted by Spamhaus.

But what about Gmail? Gmail launched 19 years ago (2004), years after competing services like Hotmail and Yahoo Mail (1996 and 1997, respectively). The Gmail service was different, and some of the differences would be natural, due to it coming along much later than other services, but also, other differences are possibly because Google has Not Invented Here (NIH) syndrome; deciding to avoid doing what everybody else is doing and trying different ways of doing things.

And does that perhaps also extend to spam filtering? Google talks at length about how Gmail's spam filtering is powered by “machine learning powered by user feedback” and they've got a hell of a huge data set to work from. More than 1.5 billion users, and they're generally the largest service represented in any B2C (consumer) email marketing list – often 60%+ of the list, meaning that if Target or Walmart has an active subscriber list of 2 million subscribers, 1.2 million of those are Gmail users, and that's a wonderfully large panel for Gmail to obtain feedback from, to determine whether or not mail from Target or Walmart should go to the spam folder or to the inbox.

It boils down to this: Gmail does not observably use any blocklists to filter or reject mail, and all that noise above is my theory as to why, which boils down to: NO. They ultimately probably don't need the simple reputation data provided by blocklists, as they've got their own data, and can draw their own conclusions. Thus,  you can't draw any conclusion about Gmail delivery based on finding your IP address or domain name on a blocklist. Gmail, simply put, does not work that way.

There are two exceptions:

First, if you're engaging in bad sending practices, both Gmail and blocklists could figure this out. They're figuring it out separately. But keep in mind that they have different sets of data that they're looking at, and the streams do not cross. In other words, if you're blocklisted on a blocklist, and you also have Gmail inbox placement issues, you got “caught” by two totally separate and unrelated systems. They are not connected.

Next, Google MIGHT utilize some data from Spamhaus in some way. They clearly do not subscribe to Spamhaus ZEN or the DBL; you're never going to see a bounce from sending to a Gmail user that directly and clearly suggests that your sending IP address is on a Spamhaus blocklist. But there are a number of us in this whole “deliverability industry” thing who suspect that Spamhaus reputation data might be one of the many things that feeds into the black box that is the spam filtering engine at Gmail, based on our observations over the years. Though I'm not the only one who thinks this, take it all with a grain of salt. We could be confusing correlation and causation. But…. I do suspect that senders with Spamhaus issues are probably going to find it more difficult to deliver mail to Gmail, and I do suspect an underlying connection.

Official confirmation is not on the table. I occasionally talk to folks at Spamhaus, and I've certainly talked to a person or two at Google over the years. But I'm not going to ask either of them about this, because if there's anything there, they're not going to talk about it.



  1. You should send this to that guy on Reddit...

  2. In August 2021, an email sent from my mailserver to Gmail bounced with a bounce message that said, "The IP you're using to send mail is not authorized to send email directly to our servers." I found my server was listed on Spamhaus' Policy Block List and removed it and 10 minutes later, maybe an hour after the bounce, Gmail accepted an email from my server. I have kept my IP address off of the Spamhaus PBL since then and have not seen that bounce message again.

    This strongly suggests Spamhaus is connected somehow to Gmail's spam filtering.


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