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Make senders work to get into your inbox

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Hi HN :) really excited to share this with you.The one thing AI reliably does is generate noise. Half the tools I see launch are just machines for producing more noise across more channels. And people are starting to see this in the form of emails in their inboxes as spam filters are struggling.There used to be a useful signal in email: the effort a sender put into customizing a message was a rough proxy for how relevant it actually was. AI killed that. Now it's customized slop with the appearance of effort with none of the cost. It is painful that the open internet / open channels have been abused like this.Captchainbox applies the idea of proof-of-work to email. If a sender is willing to do a bit of work to reach you, the message is more likely to be worth your time and the sender more likely to be real. The work is a traditional captcha. You can also set a pay-to-deliver amount if you want more friction. The proceeds of the delivery payment after transaction costs go to the Internet Archive and the EFF. The tool currently works by authing with your Gmail or Outlook and during launch time I make this completely free as a lifetime deal (with optional payment if you wanna support).How it works: Captchainbox builds a whitelist automatically from the metadata of your past correspondence. If you've emailed an individual address, that sender can reach you. If you talk to several people at the same domain, we whitelist the whole domain. If one transactional-looking sender has sent you more than 10 emails, we treat it as a transactional domain and let it through. This whitelist is for you to change whenever you want. It continues to build organically as you converse with more addresses.Incoming mail is checked against that whitelist. Senders already on it land in your inbox as normal. Anyone else gets archived (never deleted) and is sent a challenge. This can be the captcha or the payment link. Once they solve it, their email is pulled out of the archive and put back into your inbox.if you want to see what this looks like from a sender's point of view, send me an email here: [email protected] service only ever reads metadata, never message content. And since nothing is ever deleted, you can't lose a message. There is a legitimate risk / downside: if you sign up to a new service, these emails also land in the archive. Since we do not process the content, a first-time sender who can't solve the challenge (say an automated activation email) will sit in your archive until you spot it.Happy to answer anything! :)

HN · launched Jul 15, 2026 · 44 upvotes (top 17%) · 0 views

Niche: ai and productivity email clients · 126 launches, 8 in the last 7 days ▼ -43% · Explore this niche →

Category and tags

  • Horizontal
  • Communication
  • B2C
  • Not AI
  • Commercial product

Visit website ↗ Source listing ↗

Could you build this?

Yes Captchainbox uses OAuth with Gmail/Outlook APIs to inspect incoming sender headers and redirects unknown senders to a Stripe checkout link before releasing the email, which is composed of standard SaaS APIs and email webhooks.

Discussion

20 comments analyzed.

Competitors mentioned: O365 email filtering, Fastmail spam filtering, Apple call screening, Gumroad pay-what-you-want model

Concerns raised: Legitimate senders won't pay/solve CAPTCHA, causing missed opportunities, Pay-to-contact is negative signal about sender's offer quality, Existing spam filters (O365, Fastmail) already handle most spam well, Whitelisting new senders difficult unless reviewing archives, Phone spam is bigger problem than email spam currently

Feature requests: Pay-what-you-want pricing option instead of fixed fee, Opt-in marketing emails by default instead of opt-out

Competitors

Other products that read as similar to this one : 429 launches clear the similarity bar, closest 8 shown.

Attention rank: #85 of 430 (itself plus its competitors, highest first, normalized so YC and Product Hunt are compared fairly).

Launched 257 days after the earliest competitor.

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