Sudden Drop in Reply Rates Possibly Linked to SURBL and Suomispam Blacklists on Warmed Up Domains | Clay

Mary
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That pattern usually points to a deliverability issue, but I wouldn't assume SURBL alone is the root cause. I'd also check your domain/IP reputation, SPF/DKIM/DMARC alignment, engagement signals, and whether the warmup network is affecting sender trust. If even unused domains are showing up, it's worth auditing the warmup setup rather than just the blacklist. Quick question: are the reply drops happening across all inboxes, or only specific Google Workspace domains? Daria
Daria
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Thanks, this is really helpful Mary DNS (SPF/DKIM/DMARC) has already been reviewed by our outbound specialist, so as far as we know everything is configured correctly. When you mention checking domain/IP reputation and whether the warmup network is affecting sender trust, could you elaborate on that? Specifically:
How would you check this in practice?
Which tools would you use?
If the warmup network is indeed the main suspect, what would you consider the safest next step? Yesterday I paused warmup completely because I honestly wasn’t sure what the right thing to do was. Would you recommend moving to a different warmup provider, or is there another approach? Regarding your question: Historically, we only sent from Google Workspace, so I can’t really compare Google vs Microsoft. After we saw a significant drop in replies from our Google infrastructure, we started sending from Microsoft, but we don’t have a baseline because we hadn’t used it before. As I mentioned above, many of those Microsoft domains are blacklisted as well. The only infrastructure that isn’t blacklisted is a pre-warmed infrastructure we purchased from Instantly. However, reply rates there are also much lower than expected. There’s also another interesting pattern. Our sequence is:
Email 1 – no image
Emails 2 & 3 – with an image
Email 4 – no image
We’ve now sent around 2,000 emails. We get a couple of replies to Email 1, and then almost complete silence afterwards. It almost feels like deliverability “dies” after the first touch. These emails are slightly different from the versions we tested previously, but getting virtually zero replies at this volume is extremely unusual. That’s why I’m trying to understand whether we’re dealing with a deliverability issue rather than a copy or targeting issue.
Mary
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Thanks for the extra detail, this gives a much clearer picture. From what you've shared, I don't think I'd focus on the blacklists alone anymore. The fact that you're seeing the same pattern across your Google domains, Microsoft domains, and even Instantly's pre-warmed infrastructure makes me think this is more of a deliverability/inbox placement issue than a simple reputation problem. The biggest thing that stands out is that Email 1 gets a few replies, then the follow-ups almost completely die. If I were digging into this, I'd want to confirm where those follow-ups are actually landing first. They could be getting delivered but ending up in Spam or Promotions, especially with the images or tracking in later emails. Personally, I'd avoid changing providers just yet. I'd let the domains settle after pausing warmup, then work through it methodically, check inbox placement, review Google Postmaster and Microsoft SNDS if available, compare the headers between Email 1 and the follow-ups, and test the sequence without images or tracking. That usually makes the real issue much easier to spot than changing multiple things at once. Out of curiosity, have you done any seed inbox placement tests across Gmail and Outlook for each email in the sequence, or have you mostly been judging it from blacklist checks and reply rates? Daria
Daria
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Thanks, that’s a really good point Mary One important detail: reply rates on Email 1 have also dropped significantly compared to where they used to be. We used to see around 1.52% replies on the first email, but that later dropped to around 0.14%. That’s actually when we first started investigating deliverability. We ran inbox placement tests for Email 1 only, and they came back looking good, despite the reply rate remaining very low. Later we noticed another pattern: once prospects move into the follow-up sequence, replies almost completely disappear. Regarding the pre-warmed Instantly infrastructure, one theory from my outbound specialist is that the lower reply rates could simply be because those domains aren’t branded. I’m not fully convinced that branding alone could explain such a dramatic difference, but I’d be interested in your opinion. Based on everything you’ve seen, would you still prioritize running inbox placement tests for each email in the sequence?
Mary
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From 1.52% → 0.14%. That's roughly a 90% drop in reply rate. Daria
Daria
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Yes
Mary
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The fact that Email 1 dropped from 1.52% to 0.14% before you noticed the follow-ups going quiet makes me think the follow-ups are probably a symptom, not the root cause. Since your inbox placement test for Email 1 looked healthy, I wouldn't jump straight to saying it's only a deliverability issue. At this point, I'd be looking at the bigger picture, sender reputation over time, engagement signals, any changes to the sequence or targeting, and then how the follow-ups are being treated. I would still test every email in the sequence though. Just because Email 1 lands in the inbox doesn't mean Email 2, 3, or 4 are being treated the same. The images alone make them different enough that it's worth validating each step instead of assuming they'll behave the same. As for the Instantly infrastructure, I do think branded domains tend to perform better over time because they're more trustworthy to recipients, but I don't think branding by itself explains a drop that dramatic. It feels like there's another variable in the mix. One thing I'd really want to understand is what changed around the time the reply rate started falling. Was it the lead source, the copy, sending volume, personalization, tracking, or something else? In my experience, that's usually where the real answer is hiding.
Mary
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Daria
asawa.fms
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