Make unknown senders pay to reach you.
Their message stays out of your inbox until they pay the price you choose. Trusted contacts get through as usual. Completely free to use.
Put a price on unsolicited access
Your attention has value. Unknown senders should prove theirs.
Spam filters catch obvious junk. Personalized cold outreach still consumes your time. Captchainbox makes senders put money behind the interruption.
Sarah Chen
nowsarah@designco.com
Re: new design direction
Step 01
Sign in with your service.
Captchainbox checks your conversation metadata. We never read your messages. We build a trusted contacts and accounts list for you.
Sign in with your serviceGmail connected
you@gmail.com
Analyzed
2,847
Trusted
284
Status
Active
Step 02
Every sender checked silently.
For every new message Captchainbox checks the sender against your trusted contacts. Unknown senders are held safely and receive a pay to deliver link. Introductions through trusted contacts get through.
See how filtering worksStep 03
They pay. You decide where it goes.
The sender pays the price you set and their message is delivered. After Stripe's actual processing fee, Captchainbox keeps 10% and 90% goes to you, the Internet Archive, or the Electronic Frontier Foundation. CAPTCHA remains an optional mode.
See the verification flow in actionInbox verification
This inbox uses pay-to-deliver. Pay the price set by the recipient to get your message delivered.
Payment is the defaultPay to deliver your message
The inbox owner decides where their 90% goes after Stripe fees.
You're verified
Your message is on its way to their inbox.
Your payout, your choice
Pay yourself or fund the open internet.
Payments accumulate in your ledger. Connect Stripe to pay yourself, or direct future proceeds to the Internet Archive or the Electronic Frontier Foundation.
Stripe deducts its actual fee. Captchainbox keeps 10% of the remainder. Your selected destination receives the other 90%.
Pricing
Free to install. We earn when you earn.
No subscription for individuals. Stripe fees plus 10% of the remainder per successful payment.
For individuals
No subscription. No credit card required.
- Set your pay-to-deliver price
- Keep 90% after Stripe fees
- Pay yourself, the EFF, or Internet Archive
- Real-time inbox filtering
- Calendar invite protection
- Trusted circle from sent history
- Emails archived, never deleted
FAQ
Common questions.
What is Captchainbox?
Captchainbox makes unknown senders pay the price you set before their email reaches your inbox. Their message is held safely until they pay. People and domains you already trust get through as usual.
Is Captchainbox really free?
Yes. There is no subscription. Stripe deducts its actual processing fee from each payment, Captchainbox keeps 10% of what remains, and 90% goes to the payout destination you choose.
Where does the sender payment go?
You choose: connect your own Stripe account and pay yourself, or direct your share to the Internet Archive or the Electronic Frontier Foundation. Your choice applies to future payments and can be changed in Settings.
How is each payment split?
Stripe first deducts its actual processing fee. Captchainbox keeps 10% of the remaining amount and your selected payout destination receives the other 90%. The fee is calculated from the real Stripe transaction, not an estimate.
Does Captchainbox read my emails?
No. Captchainbox filters by sender identity only, never message content. It passed a CASA Tier 2 security assessment, the independent audit Google requires for apps accessing Gmail data.
What happens to emails from unknown senders?
They are archived, never deleted. If the sender pays, the email is moved back to your inbox automatically and the sender is trusted for a grace period. You can review held messages and whitelist senders yourself from the dashboard.
Can I use a CAPTCHA instead?
Yes. Payment is the default, but you can switch your inbox to a free CAPTCHA gate in Settings at any time.
Which email providers are supported?
Gmail and Google Workspace accounts are fully supported today via Google sign-in. Outlook support is in the works.
Make your inbox pay its way.
Set your price in minutes. Free to install, with CAPTCHA available whenever you prefer it.
Curious what senders see? Send me an email and see the pay-to-deliver flow yourself.