Captchainbox - Make senders work to get into your inbox

Stop AI spam from flooding your inbox and calendar. Unknown senders solve a CAPTCHA or pay a fee to get in. Trusted contacts get through as usual.

Free for individuals · 5-minute setup · Archived, never deleted

0 emails screened·0 unwanted emails stopped

Built for inboxes overwhelmed by AI outreach

AI cold outreach is nearly free.
Make senders work for your time and attention.

Spam filters catch the obvious, but mass-customized outreach gets through. You miss what matters and drown in what you didn't ask for.

Step 01

Sign in with your email provider.

Captchainbox scans your conversation metadata. We never read your messages. We build a trusted sender and domains list for you.

Step 02

Every sender checked silently.

For every new email Captchainbox checks the sender against your trusted contacts. Unknown senders are archived (never deleted) and sent a verification link. Introductions through trusted contacts get through.

See how filtering works

Step 03

Senders show they are worth your time and attention.

Unknown senders verify through a CAPTCHA or pay a small fee to show they are relevant to you. They complete the verification and their email is delivered to your inbox. Payment fees get pooled and donated.

See the verification flow in action

Proceedings are donated to

Pooled and donated annually, 50/50. See the ledger.

Pricing

Simple pricing to get back your time and attention.

Free for individuals, no credit card required.

Teams

Want Captchainbox for your whole team? Let's talk.

Reach out

What is Captchainbox?

Captchainbox is an email CAPTCHA for your inbox. Emails from unknown senders are moved out of your inbox and the sender receives an automatic reply with a quick verification challenge. Once they verify, their email lands back in your inbox — bots and mass cold-email tools never make it through.

Is Captchainbox really free?

Yes. Captchainbox is free for individuals — no credit card, no trial, no catch. Teams can reach out for a custom setup.

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 verifies, the email is moved back to your inbox automatically and the sender is trusted for a grace period. You can also review everything and whitelist senders yourself from the dashboard.

What does a sender have to do to reach me?

They get an automatic reply with a link, click it, and complete a quick human-verification check. It takes under 30 seconds. Real people get through easily; automated outreach tools almost never bother.

Which email providers are supported?

Gmail and Google Workspace accounts are fully supported today via Google sign-in. Outlook support is in the works.

Take back your inbox.

Set up in 5 minutes. Free to get started.